FineTurbo_User_manual User Manual FINETurbo
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User Manual FINE™/Turbo v8.10 Flow Integrated Environment - November 2012 - NUMERICAL MECHANICS APPLICATIONS User Manual FINE™/Turbo v8.10 Documentation v8.10c NUMECA International Chaussée de la Hulpe, 189 1170 Brussels Belgium Tel: +32 2 647.83.11 Fax: +32 2 647.93.98 Web: http://www.numeca.com NUMERICAL MECHANICS APPLICATIONS Contents CHAPTER 1: Getting Started 1-1 Overview 1-2 Introduction Components Multi-Tasking Project Management 1-3 How To Use This Manual Outline Conventions 1-4 First Time Use Basic Installation Expert Graphics Options 1-5 How to start the FINE™/Turbo Interface 1-6 Required Licenses Standard FINE™/Turbo License Additional Licenses CHAPTER 2: Graphical User Interface 2-1 Overview 2-2 Project Selection Create New Project Open Existing Project Grid Units & Project Configuration 2-3 Main Menu Bar File Menu Mesh Menu Solver Menu Modules Menu 2-4 Icon Bar File Buttons Grid Selection Bar Solver Buttons Module Buttons User Mode 2-5 Computation Management 2-6 Graphical Area Management Configuration Management Parameters Management View Area Mesh Information Parameters Area Graphics Area Viewing Buttons 2-7 Profile Management FINE™/Turbo 1-1 1-1 1-1 1-1 1-2 1-2 1-4 1-4 1-4 1-5 1-5 1-5 1-6 1-7 1-7 1-7 2-1 2-1 2-2 2-2 2-4 2-4 2-6 2-6 2-9 2-11 2-12 2-12 2-12 2-13 2-14 2-14 2-14 2-14 2-15 2-15 2-16 2-16 2-18 2-18 2-19 2-19 2-22 iii Contents CHAPTER 3: Fluid Model 3-1 Overview 3-2 The Fluid Model in the FINE™/Turbo GUI Properties of Fluid Used in the Project List of Fluids Add Fluid Delete Fluid from List Edit Fluid Show Fluid Properties Filters Import Fluid Database Expert Parameters CHAPTER 4: Flow Model 4-1 Overview 4-2 Mathematical Model Euler Laminar Navier-Stokes Turbulent Navier-Stokes Expert Parameters for Turbulence Modelling Best Practice for Turbulence Modelling Laminar-Transition Model Gravity Forces Low Speed Flow (Preconditioning) 4-3 Characteristic & Reference Values Reynolds Number Related Information Reference Values CHAPTER 5: Boundary Conditions 5-1 Overview 5-2 Boundary Conditions in the FINE™/Turbo GUI Inlet Condition Outlet Condition Periodic Condition Solid Wall Boundary Condition External Condition (Far-field) 5-3 Expert Parameters Imposing Velocity Angles of Relative Flow Inlet Mass Flow Boundary Condition Outlet Mass Flow Boundary Condition Outlet Averaged Mach Number Boundary Condition Control of backflows Torque and Force Euler or Navier-Stokes Wall for Viscous Flow Pressure Condition at Solid Wall 5-4 Best Practice for Imposing Boundary Conditions iv 3-1 3-1 3-2 3-2 3-2 3-3 3-9 3-9 3-10 3-10 3-10 3-10 4-1 4-1 4-2 4-2 4-2 4-2 4-4 4-9 4-19 4-21 4-22 4-22 4-22 4-23 5-1 5-1 5-1 5-4 5-7 5-11 5-12 5-16 5-17 5-17 5-17 5-17 5-18 5-18 5-18 5-18 5-19 5-19 FINE™/Turbo Contents Compressible Flows Incompressible or Low Speed Flow Special Parameters (for Turbomachinery) CHAPTER 6: Numerical Scheme 6-1 Overview 6-2 Numerical Model Introduction Numerical Model in the FINE™/Turbo GUI Expert Parameters 6-3 Time Configuration Interface for Unsteady Computation Expert Parameters for Unsteady Computations Best Practice on Time Accurate Computations CHAPTER 7: Physical Models 7-1 Overview 7-2 Fluid-Particle Interaction Introduction Fluid-Particle Interaction in the FINE™/Turbo GUI Specific Output Expert Parameters 7-3 Fluid-Structure Thermal Mechanical 7-4 Passive Tracers Boundary Conditions Initial Solution Outputs 7-5 Porous Media Model Porous Media Model in the FINE™/Turbo GUI Experts Parameters 7-6 Cavitation Model Cavitation Model in the FINE™/Turbo GUI Experts Parameters CHAPTER 8: Dedicated Turbomachinery Models 8-1 Overview 8-2 Rotating Blocks 8-3 Rotor/Stator Interaction Rotor/Stator Interfaces in the FINE™/Turbo GUI How to Set-up a Simulation with Rotor/Stator Interfaces? 8-4 Harmonic Method Introduction Interface & Best Practice for Harmonic Computations Expert Parameters FINE™/Turbo 5-19 5-20 5-20 6-1 6-1 6-1 6-1 6-2 6-5 6-10 6-10 6-13 6-14 7-1 7-1 7-1 7-1 7-3 7-7 7-8 7-9 7-9 7-13 7-23 7-23 7-23 7-24 7-24 7-24 7-24 7-25 7-25 7-25 8-1 8-1 8-1 8-4 8-4 8-6 8-19 8-19 8-20 8-27 v Contents 8-5 Clocking Introduction Interface Settings 8-6 Cooling/Bleed Introduction Cooling/Bleed Model in the FINE™/Turbo GUI Expert Parameters Cooling/Bleed Data File: ’.cooling-holes’ 8-7 Rigid Motion 8-8 Aeroacoustics Aeroacoustics in the FINE™/Turbo GUI Expert Parameters for Aeroacoustics 8-9 Laminar-Transition Model Introduction Transition Model in the FINE™/Turbo GUI Expert Parameters 8-10 Performance Curve Introduction Performance Curve in the FINE™/Turbo GUI 8-11 SubProject Management Introduction Set-up of SubProjects in FINE™/Turbo CHAPTER 9: Initial Solution 9-1 Overview 9-2 Block Dependent Initial Solution How to Define a Block Dependent Initial Solution Examples for the use of Block Dependent Initial Solution 9-3 Initial Solution Defined by Constant Values 9-4 Initial Solution from File General Restart Procedure Restart in Unsteady Computations Expert Parameters for an Initial Solution from File 9-5 Initial Solution for Turbomachinery Methodology Grouping & Parameters Expert Parameters 9-6 Throughflow-oriented Initial Solution CHAPTER 10:Output 10-1 Overview 10-2 Output in FINE™/Turbo Computed Variables Surface Averaged Variables Azimuthal Averaged Variables Template manager ANSYS vi 8-30 8-30 8-31 8-33 8-33 8-34 8-54 8-54 8-59 8-59 8-60 8-62 8-63 8-63 8-63 8-65 8-66 8-66 8-66 8-69 8-69 8-70 9-1 9-1 9-1 9-2 9-2 9-3 9-3 9-3 9-5 9-5 9-5 9-6 9-7 9-8 9-8 10-1 10-1 10-2 10-2 10-8 10-10 10-11 10-13 FINE™/Turbo Contents Global Performance Output Plot3D Formatted Output 10-3 Expert Parameters Azimuthal Averaged Variables Global Performance Output Solid Data Output CHAPTER 11:Task Manager 11-1 Overview 11-2 Getting Started PVM Daemons Multiple FINE™/Turbo Sessions Machine Connections Remote Copy Features on UNIX/LINUX Remote Copy Features on Windows 11-3 The Task Manager Interface Hosts Definition Tasks Definition 11-4 Parallel Computations Introduction Management of Inter-Block Communication How to Run a Parallel Computation Use an External OpenMPI Library on LINUX/UNIX Troubleshooting Limitations 11-5 Task Management in Batch Launch IGG™ in Batch Launch AutoGrid™ in Batch Launch FINE™ in Batch Launch the flow solver in Sequential Mode in Batch Launch the flow solver in Parallel Mode in Batch Launch CFView™ in Batch 11-6 Limitations CHAPTER 12:Computation Steering & Monitoring 12-1 Overview 12-2 Control Variables Control Variables in the FINE™/Turbo GUI Expert Parameters 12-3 Convergence History Convergence History in the FINE™/Turbo GUI Expert Parameters 12-4 MonitorTurbo Introduction The MonitorTurbo GUI 12-5 Best Practice for Computation Monitoring Introduction FINE™/Turbo 10-19 10-22 10-22 10-22 10-23 10-24 11-1 11-1 11-1 11-1 11-2 11-2 11-4 11-4 11-5 11-5 11-6 11-17 11-17 11-19 11-19 11-20 11-21 11-22 11-22 11-22 11-23 11-24 11-30 11-31 11-43 11-45 12-1 12-1 12-1 12-1 12-2 12-3 12-3 12-10 12-10 12-10 12-11 12-14 12-14 vii Contents Convergence History MonitorTurbo Analysis of Residuals APPENDIX A:File Formats A-1 Overview A-2 Files Produced by IGG™ The Identification File: ’project.igg’ The Binary File: ’project.cgns’ The Geometry File: ’project.geom’ The Boundary Condition File: ’project.bcs’ The Configuration File: ’project.config’ A-3 Files Produced by the FINE™/Turbo GUI The Project File: ’project.iec’ The Computation File: ’project_computation.run’ A-4 Files Produced by the FINE™/Turbo solver The Binary Solution File: ’project_computation.cgns’ The Global Solution File: ’project_computation.mf’ The Global Solution File: ’project_computation.xmf’ The Residual File: ’project_computation.res’ The LOG File: ’project_computation.log’ The STD file: ’project_computation.std’ The Wall File: ’project_computation.wall’ The AQSI File: ’project_computation.aqsi’ The ADF File: ’project.adf’ The Plot3D Files The Meridional File: ’project_computation.me.cfv’ A-5 Files Used as Data Profile Boundary Conditions Data Fluid Properties Solid Properties A-6 Resource Files Boundary Conditions Resource File: ’euranus_bc.def’ Fluids Database File: ’euranus.flb’ Units Systems Resource File: ’euranus.uni’ APPENDIX B:List of Expert Parameters B-1 Overview B-2 List of Integer Expert Parameters B-3 List of Float Expert Parameters APPENDIX C:Characteristics of Thermodynamic Tables C-1 Overview C-2 Main Characteristics for Water (Steam) C-3 Main Characteristics for R134a viii 12-14 12-16 12-16 A-1 A-1 A-1 A-2 A-2 A-2 A-2 A-2 A-2 A-2 A-3 A-3 A-3 A-7 A-7 A-8 A-9 A-10 A-10 A-10 A-10 A-10 A-11 A-11 A-12 A-14 A-14 A-15 A-15 A-15 A-15 B-1 B-1 B-1 B-3 C-1 C-1 C-1 C-2 FINE™/Turbo Contents APPENDIX D:TabGen D-1 Overview D-2 Graphical User Interface Start Program Main Window D-3 Launch TabGen in Batch Mode FINE™/Turbo D-1 D-1 D-2 D-2 D-4 D-9 ix Contents x FINE™/Turbo CHAPTER 1: 1-1 Getting Started Overview Welcome to the FINE™/Turbo User Manual, a presentation of NUMECA’s Flow INtegrated Environment for computations on structured meshes. This chapter presents the basic concepts of FINE™/Turbo and shows how to get started with the program by describing: • what FINE™/Turbo does and how it operates, • how to use this guide, • how to start the FINE™/turbo interface. 1-2 Introduction 1-2.1 Components The resolution of Computational Fluid Dynamics (CFD) problems involves three main steps: • spatial discretization of the flow domain, • flow computation, • visualization of the results. To perform these steps NUMECA has developed three software systems. The first one, IGG™, is an Interactive Geometry modeller and Grid generation system for multiblock structured grids. The second software system, the FINE™/turbo solver, is a state of the art 3D multiblock flow solver able to simulate Euler or Navier-Stokes (laminar or turbulent) flows. The third one, CFView™, is a highly interactive Computational Field Visualization system. These three software systems have been integrated in a unique and user friendly Graphical User Interface (GUI), called FINE™/Turbo, allowing the achievement of complete simulations of 3D internal and external flows from the grid generation to the visualization, without any file manipulation, through the concept of project. Moreover, multi-tasking capabilities are incorporated, allowing the simultaneous treatment of multiple projects. FINE™/Turbo 1-1 Getting Started Introduction 1-2.2 Multi-Tasking FINE™/Turbo has the particularity of integrating the concept of multi-tasking. This means that the user can manage a complete project in the FINE™/Turbo interface; making the grid using IGG™, running the computation with the FINE™/Turbo solver and visualizing the results with CFView™. Furthermore, the user has the possibility to start, stop and control multiple computations. Please note that the flow simulation can be time consuming, therefore the possibility of running computations in background has been implemented. See Chapter 11 for more detail on how to manage multiple tasks through the interface or in background. 1-2.3 Project Management To manage complete flow analyses, FINE™/Turbo integrates the concept of project. A project involves grid generation, flow computation and visualization tasks. The results of each of these tasks are stored in different files that are automatically created, managed and modified within FINE™/Turbo: • The grid files: The grid generation process, IGG™, creates files containing the representation of the geometry and the grid related to the project. The definition of the types of boundary conditions is also done during this process. The five files that contain the information about the mesh have the extensions ".igg", ".geom", ".bcs", ".config" and ".cgns". • The project file: The project file is created by FINE™/Turbo. It has the extension ".iec" and contains the input parameters needed for the flow computations. • The result files: FINE™/Turbo creates a new subdirectory for each computation where it stores the following files: — a file with extension ".run" containing all computation input parameters used by the solver and by CFView™, — a ".cgns" file that contains the solution and that is used for restarting the solver, — a ".res" file used by the Monitor to visualize the residual history (see Chapter 12), — two files used to visualize the convergence history in the Steering with extensions ".steering" and ".steering.binary" (see Chapter 12). — two files with extensions ".mf" and ".wall" that contain global solution parameters. — a ".xmf" file that stores the information contained in the ".mf" file in XML format. — two files with extensions ".std" and ".log" that contain information on the flow computation process. — a ".batch" file used to launch the computation in batch (see Chapter 11). • The CFView™ visualization files: In addition to the ".run" file, the flow solver creates a series of files, which can be read by CFView™. These files have different extensions. For example in case of turbomachinery flow problem, the solver will create a file for the azimuthal averaged results with extension ".me.cfv". Through the interface, the user can modify all the information stored in the files associated to the project. When creating a new project a new directory is made, e.g. "/project". In this directory the project file is stored "/project/project.iec" and a directory is created called "/project/_mesh". In this directory the grid files used for the computations can be stored. It is however also possible to select a grid that is located in another directory. Only one mesh file should be used for all computations in a project. If computations need to be done on another mesh file it is advised to duplicate the project (see section 2- 1-2 FINE™/Turbo Introduction Getting Started 3.1.4) or to create a new project (see section 2-3.1.1) for those computations. The special characters, such as ü, ë and ê et al., are not allowed in the path name. Off line files on Windows operation system are not supported. The length of the path name should be less than 256. FIGURE 1.2.3-1 Example of file management for a FINE™/Turbo project Both the absolute and relative path names are used in ".iec" and ".run" files for the mesh and initial solution files. When moving the project from one location to another location in the local machine or between different machines (the same or different OS), the use of the relative pathnames allows the user to: • open the graphical user interface and (re)start calculation without the need to (re)link the mesh and pathnames, • open a solution file within CFView™ without the need to open the graphical user interface, • start calculations in batch mode without the need to open the graphical user interface and (re)link the mesh and pathnames. The limitations on the use of relative pathnames are as follows: • All files (mesh and computations) related to a given project must be located in hard-coded subdirectories (e.g. _mesh). • Keywords related to relative path in ".iec" and ".run" files are only vaild if the concerned files are at the same level of the project file ".iec" or in subdirectories. • Both the project and the directory in which it is included must have the same name. They can’t be renamed. • When duplicating or moving the project, the user must be able to copy either the entire project (mesh files and computations with existing solutions), or a partial project (mesh files and computations, restricted to ".run" files) FINE™/Turbo 1-3 Getting Started How To Use This Manual • Relative path is not compatible with FINE™/Design3D. 1-3 How To Use This Manual 1-3.1 Outline This manual consists of five distinct parts: • • • • • • • Chapters 1 and 2: introduction and description of the interface, Chapters 3 to 10: computation definition, Chapter 11: task management, Chapter 12: monitoring capabilities, Appendix A: used file formats, Appendix B: list of supported non-interfaced expert parameters, Appendix C: characteristics of steam tables. At first time use of FINE™/Turbo it is recommended to read this first chapter carefully and certainly section 1-4 to section 1-6. Chapter 2 gives a general overview of the FINE™/Turbo interface and the way to manage a project. For every computation the input parameters can be defined as described in the Chapters 3 to 10. Chapter 11 gives an overview of how to run computations using the Task Manager or using a script. Chapter 12 finally describes the available tools to monitor the progress on a computation. In Chapters 3 to 10, the expert user finds a section describing advanced options that are available in expert user mode. Additionally Appendix B provides a list with all supported expert parameters on the page Computation Steering/Control Variables in expert user mode. For each parameter a reference is given to the section in the manual where it is described. The use of non-supported parameters is at own risk and will not guarantee correct results. 1-3.2 Conventions Some conventions are used to ease information access throughout this guide: • • • • • Commands to type are in italics. Keys to press are in italics and surrounded by <> (e.g.: press). Names of menu or sub-menu items are in bold. Names of buttons that appear in dialog boxes are in italics. Numbered sentences are steps to follow to complete a task. Sentences that follow a step and are preceded with a dot (•) are substeps; they describe in detail how to accomplish the step. The hand indicates an important note The pair of scissors indicates a keyboard short cut. 1-4 FINE™/Turbo First Time Use Getting Started A light bulb in the margin indicates a section with a description of expert parameters. 1-4 First Time Use 1-4.1 Basic Installation When using FINE™/Turbo for the first time it is important to verify that FINE™/Turbo is properly installed according to the installation note. The installation note provided with the installation software should be read carefully and the following points are specifically important: • Hardware and operating system requirements should be verified to see whether the chosen machine is supported. • Installation of FINE™/Turbo according to the described procedure in a directory chosen by the user and referenced in the installation note as ‘NUMECA_INSTALLATION_DIRECTORY’. • A license should be requested that allows for the use of FINE™/Turbo and the desired component and modules (see section 1-6 for all available licenses). The license should be installed according to the described procedure in the installation note. • Each user willing to use FINE™/Turbo or any other NUMECA software must perform a user configuration as described in the installation note. When these points are checked the software can be started as described in the installation note or section 1-5 of this user manual. 1-4.2 Expert Graphics Options a) Graphics Driver The graphics area of the FINE™/Turbo interface uses by default an OPENGL driver that takes advantage of the available graphics card. When the activation of OPENGL is causing problems, FINE™/Turbo uses an X11 driver (on UNIX) or MSW driver (for Windows) instead. It is possible to explicitly change the driver used by FINE™/Turbo in the following ways: On UNIX: in csh, tcsh or bash shell: setenv NI_DRIVER X11 in korn shell: NI_DRIVER=X11 export NI_DRIVER The selection will take effect at the next session. On Windows: • Log in as Administrator. • Launch regedit from the Start/Run menu. • Go to the HKEY_LOCAL_MACHINE/SOFTWARE/NUMECA International/Fine# register. • Modify the DRIVER entry to either OPENGL or MSW. FINE™/Turbo 1-5 Getting Started How to start the FINE™/Turbo Interface The selection will take effect at the next session. b) Background Color The background color of the graphics area can be changed by setting the environment variable NI_IGG_REVERSEVIDEO on UNIX/LINUX platforms or IGG_REVERSEVIDEO on Windows platforms. Set the variable to ’ON’ to have a black background and set it to ’OFF’ to have a white background. The variable can be manually specified through the following commands: On UNIX: in csh, tcsh or bash shell: setenv NI_IGG_REVERSEVIDEO ON in korn shell: NI_IGG_REVERSEVIDEO=ON export NI_IGG_REVERSEVIDEO The selection will take effect at the next session. On Windows: • Log in as Administrator. • Launch System Properties from the Start/Settings/Control Panel/System menu. • Go in the Environment Variables. • Modify or add the IGG_REVERSEVIDEO entry to either ON or OFF. The selection will take effect at the next session. 1-5 How to start the FINE™/Turbo Interface In order to run FINE™/Turbo, the following command should be executed: On UNIX and LINUX platforms type: fine -print When multiple versions of FINE™/Turbo are installed the installation note should be consulted for advice on how to start FINE™/Turbo in a multi-version environment. On Windows click on the FINE™/Turbo icon in Start/Programs/NUMECA software/fine#. Alternatively FINE™/Turbo can be launched from a dos shell by typing: \fine#\bin\fine where NUMECA_INSTALLATION_DIRECTORY is the directory indicated in section 1-4.1 and # is the number corresponding to the version to be used. 1-6 FINE™/Turbo Required Licenses Getting Started 1-6 Required Licenses 1-6.1 Standard FINE™/Turbo License The standard license for FINE™/Turbo allows for the use of all basic features of FINE™/Turbo including: • IGG™ (see separate IGG™ manual), • AutoGrid™ (see separate AutoGrid™ manuals), • CFView™ (see separate CFView™ manual), • Task Manager (see Chapter 11), • Monitor (see Chapter 12). 1-6.2 Additional Licenses Within FINE™/Turbo the following features are available that require a separate license: • parallel computations (see Chapter 11), • treatment of unsteady rotor-stator interfaces (see Chapter 8), • harmonic method (see Chapter 8), • transition (see Chapter 4 and Chapter 8), • fluid-particle interaction (see Chapter 7), • passive tracers (see Chapter 7), • conjugate heat transfer (see Chapter 7), • thermodynamic tables (see Chapter 3), • cooling/bleed flow (see Chapter 8), • ANSYS outputs (see Chapter 10), • SubProject module (see Chapter 8), • porous media (see Chapter 7), • cavitation module (see Chapter 7). • MpCCI Coupling (Chapter 7) • Modal Coupling (Chapter 7) • Mesh Deformation (Chapter 7) • Aeroacoustics (Chapter 8) • CPU Booster (Chapter 6) Next to FINE™/Turbo other products are available that require a separate license: • FINE™/Design 3D (3D inverse design, see separate user manual). FINE™/Turbo 1-7 Getting Started 1-8 Required Licenses FINE™/Turbo CHAPTER 2: 2-1 Graphical User Interface Overview When launching FINE™/Turbo as described in Chapter 1 the interface appears in its default layout as shown in Figure 2.1.0-1. An overview of the complete layout of the FINE™/Turbo interface is shown on the next page in Figure 2.1.0-2. In the next sections the items in this interface are described in more detail. Together with the FINE™/Turbo interface a Project Selection window is opened, which allows to create a new project or to open an existing project. See section 2-2 for a description of this window. To define a profile through the FINE™/Turbo interface a Profile Manager is included. The Profile Manager is described in more detail in section 2-7. FIGURE 2.1.0-1 Default FINE™/Turbo FINE™/Turbo Interface 2-1 Graphical User Interface Project Selection Grid Configuration (under license) Main menu bar Icon bar Computations button Parameters button View button Mesh information Parameters area FIGURE 2.1.0-2 Complete 2-2 Graphics area overview of the FINE™/Turbo interface Project Selection When the FINE™/Turbo interface is started the Project Selection window is appearing together with the interface. This window allows to create a new project or to open an existing one as described in the next sections. After use of this window it is closed. To open a project or to create a new one without the Project Selection window is also possible using the File menu. 2-2.1 Create New Project To create a new project when launching the FINE™/Turbo interface: 1. click on the Create a New Project... icon ( ) in the Project Selection dialog box. A File Chooser will appear, which allows to select a name and location for the new project. The layout of the File Chooser depends on the used operating system but a typical layout is shown in Figure 2.2.1-3. The Directories list allows to browse through the available directory structure to the project directory. Then the Files list can be used to select the file name. In the case a file needs to be opened an existing file should be selected in the list of available files. In the case a new file needs to be created the user can type a new file name with the appropriate extension. In the List Files of Type bar the default file type is set by default to list only the files of the required type. 2-2 FINE™/Turbo Project Selection Graphical User Interface FIGURE 2.2.1-3 Typical layout of a File Chooser window 2. In the Directories text box on UNIX a name can be typed or the browser under the text box may be used to browse to an appropriate location. On Windows, the browser under the Save in text box is used to browse to an appropriate location. 3. Once the location is defined type on UNIX and on Windows a new name in the text box under respectively Files and File name, for example "project.iec" (it is not strictly necessary to add the extension ".iec", FINE™/Turbo will automatically create a project file with this extension). 4. Click on OK (on UNIX) or Save (on Windows) to accept the selected name and location of the new project. A new directory is automatically created with the chosen name as illustrated in figure below indicated by point (1). All the files related to the project are stored in this new directory. The most important of them is the project file with the extension ".iec", which contains all the project settings (Figure 2.2.1-4 - (2)). Inside the project directory FINE™/Turbo creates automatically a subdirectory "_mesh" (Figure 2.2.1-4 - (3)). (1) project directory (2) (3) automatically created "_mesh" directory (4) computation directory FIGURE 2.2.1-4 Directories 5. managed through FINE™/Turbo A Grid File Selection window (Figure 2.2.1-5) appears to assign a grid to the new project. There are three possibilities: • To open an existing grid click on Open Grid File (Figure 2.2.1-5 - 1.1). A File Chooser allows to browse to the grid file with extension ".igg". Select the grid file and press OK to accept the selected mesh. A window appears to define the Grid Units and Project Configuration (Figure 2.2.1-5 - 1.2). Set the parameters in this window as described in section 2-2.3 and click OK to accept. FINE™/Turbo 2-3 Graphical User Interface Project Selection • If the grid to be used in the project is not yet created use Create Grid File to start IGG™ (Figure 2.2.1-5 - 2.1). Create a mesh in IGG™ or AutoGrid™ (Modules/AutoGrid4 - Modules/AutoGrid5) and save the mesh in the directory "_mesh" of the new project. Click on Modules/Fine Turbo and confirm "yes" to return to the FINE™/Turbo project. Select the created mesh with the pull down menu (Figure 2.2.1-5 - 2.2) in the icon bar. A window will appear to define the Grid Units and Project Configuration. Set the parameters in this window as described in section 2-2.3 and click OK to accept. 2.2 3 1.1 2.1 1.2 FIGURE 2.2.1-5 Grid File Selection window. • When using the AutoBlade™ or FINE™/Design 3D modules it is not necessary to select a grid. In that case close the Grid File Selection window (Figure 2.2.1-5 - 3) and select Modules/AutoBlade or Modules/Design 3D menu to use these modules. 2-2.2 Open Existing Project To open an existing project the two following possibilities are available in the Project Selection window: • Click on the icon Open an Existing Project... ( ). A File Chooser will appear that allows to browse to the location of the existing project. Automatically the filter in the File Chooser is set to display only the files with extension ".iec", the default extension for a project file. • Select the project to open in the list of Recent Projects, which contains the five most recently used project files. If a project no longer exists it will be removed from the list when selected. To view the full path of the selected project click on Path... To open the selected project click on Open Selected Project. 2-2.3 Grid Units & Project Configuration The Grid Units and Project Configuration window shows some properties of the selected mesh when linking the mesh to the project: • Grid Units: the user specifies the grid units when importing a mesh. The user may define a different scale factor to convert the units of the mesh to meters. The scale factor is for instance 0.01 when the grid is in centimeters. 2-4 FINE™/Turbo Project Selection Graphical User Interface • Space Configuration: allows the user to specify whether the mesh is cylindrical or Cartesian and the dimensionality of the mesh. In case the mesh is axisymmetric the axis of symmetry should be defined. If a 2D project is created by selecting Cartesian and 2 Dimensions, the mesh must have K direction and Z direction perpendicular to the surface. Some options in FINE™/Turbo are linked to the used mesh configuration. For example, the Cartesian mesh is not compatible with some TURBO features (Rotating Blocks, Azimuthal averaged output, ...). The user should select an appropriate coordinate system according to the applications. • Use Grid Configuration: This option is only available with a special license feature (SubProjects). The user can choose whether or not to use the automatic grouping based on the grid configuration file (.config). More information on the automatic grouping can be found in Chapter 8. This choice can only be made when loading the mesh for the first time, it cannot be changed afterwards. FIGURE 2.2.3-6 Grid FINE™/Turbo Units & Project Configuration window The mesh properties are always accessible after linking the mesh to the project through the menu Mesh/Properties... 2-5 Graphical User Interface 2-3 Main Menu Bar 2-3.1 File Menu Main Menu Bar 2-3.1.1 New Project The menu item File/New allows to create a new FINE™/Turbo project. When clicking on File/New a File Chooser window appears. Browse in the Directory list to the directory in which to create a new project directory (in the example of Figure 2.2.1-4 the directory "/home" was selected). Give a new name for the project in the File list, for example "project.iec" and click on OK to create the new project. When starting a new project a new directory is automatically (Figure 2.2.1-4) created with the chosen name (1). All the files related to the project are stored in this new directory. The most important of them is the project file with the extension ".iec", which contains all the project settings (2). Inside the project directory FINE™/Turbo creates automatically a subdirectory "_mesh" (3). As all the computations of the project must have the same mesh it is advised to store the mesh in this specially dedicated directory. Each time the user creates a new computation, a subdirectory is added (4). The output files generated by the flow solver will be written in the subdirectory of the running computation. After the new project is created a Grid File Selection window (Figure 2.2.1-5) appears to assign a grid to the new project. There are two possibilities: • To open an existing grid click on Open Grid File. A File Chooser allows to browse to the grid file with extension .igg. Select the grid file and press OK to accept the selected mesh. A window appears to define the Grid Units and Project Configuration. Set the parameters in this window as described in section 2-2.3 and click OK to accept. • If the grid to be used in the project was not yet created use Create Grid File to start IGG™. Create a mesh in IGG™ or AutoGrid™ (Modules/AutoGrid4 - Modules/AutoGrid5) and save the mesh in the directory "_mesh" of the new project. Click on Modules/Fine Turbo and confirm "yes" to return to the FINE™/Turbo project. Select the created mesh with the pull down menu in the icon bar. A window will appear to define Grid Units and Project Configuration. Set the parameters in this window as described in section 2-2.3 and click OK to accept. If the name of an already existing project is specified, this project file will be overwritten. All other files and subdirectories will remain the same as before. By default, no IGG™ file is associated with the new project and it is indicated "usr/ unknown" in the place of the grid file name. The procedure to link a mesh file to the project is explained in section 2-4.2. 2-3.1.2 Open Project There are two ways to open an existing project file: a) Use File/Open Menu 2-6 1. Click on File/Open. 2. A File Chooser window appears. 3. Browse through the directory structure to find the project file to open. This file has normally the ".iec" extension. If this is not the case, the file filter in the input box named 'List Files of Type', has to be modified. FINE™/Turbo Main Menu Bar 4. Graphical User Interface Select the project file. Click on the file name and press the OK button. The opened project becomes the active project. All subsequent actions will be applied to this project. 5. b) Select File From the List of Files in File Menu. The File menu lists the names of the five most recent projects that have already been opened. Click on a project name from this menu to open this project. FINE™/Turbo will check the write permission of the project directory and the project file and will issue a warning if the project or directory is read only. In both cases the project can be modified, but the changes will not be saved. Only one project can be active. Opening a second project will save and close the first one. An attempt to open a no longer existing project will remove its name from the list in the File menu. 2-3.1.3 Save Project The File/Save menu item stores the project file (with extension ".iec") on disk. The project file is automatically saved when the flow solver is started and can be saved when FINE™/Turbo is closed or when another project is opened. 2-3.1.4 Save As Project File/Save As is used to store the active project on disk under different name. A File Chooser opens to specify the new directory and name of the project. When this is done a dialog box asks whether to save all the results files associated with the project. If deactivated, only the project file (with the extension ".iec") will be saved in the new location. 2-3.1.5 Save Run Files File/Save Run Files is used to store all the information needed for the flow solver in the ".run" file of the active computation (highlighted in blue in the Computations list). This menu is mainly useful when the Task Manager is used (see Chapter 11 for a detailed description of the Task Manager). FINE™/Turbo Together with the ".run" file, a ".batch" (UNIX) or ".bat" (Windows) file is saved. This file can be used to launch the computation in batch mode, without the need of opening 2-7 Graphical User Interface Main Menu Bar the interface. More information on how to use this ".batch" file can be found in Chapter 11. If more than one computation is selected in the Computations list, then all parameters in the Parameters area will be assigned to all selected (active) computations. This may be dangerous if the parameters for the currently opened information page are not the same for all the selected computations. To avoid this it is recommended to select only one computation at a time. The ".run" file is automatically updated (or created if not existing) when starting a computation through the main menu (Solver/Start...). 2-3.1.6 Preferences When clicking on File/Preferences... the Preferences window appears and gives access to some project specific and global settings: a) Project Units In this section the user can change the units system of the project. The units can be changed independently for a selected physical quantity or for all of them at the same time. To change the units for one specific quantity select the quantity in the list (see (1) in Figure 2.3.1-7). Then select the unit under Select New Units (2). To change the units for all physical quantities at the same time use the box Reset Units System To (3). The default system proposed by NUMECA is the standard SI system except for the unit for the rotational speed, which is [RPM]. When the user changes the units, all the numerical values corresponding to the selected physical quantity are multiplied automatically by the appropriate conversion factor. The numerical values are stored into the project file ".iec" in the same units as they appear in the interface (e.g. the rotation speed is in [RPM]), but in the ".run" file, which is used by the flow solver, the numerical values are always stored in SI units (e.g the rotation speed is in [rad/s]). The results can be visualized with the flow visualization system CFView™ in the units specified in FINE™/Turbo.The change of the units can be done at any stage of the creation of the project. User-defined units can be defined through a text file "euranus.uni". Please contact our local support office for more information. (2) (3) (1) FIGURE 2.3.1-7 Project 2-8 Units in the Preferences Window FINE™/Turbo Main Menu Bar Graphical User Interface b) Global Layout In this section, the user may specify project independent preferences for the layout of the interface. More specifically the user may activate or deactivate the balloon help (Show Balloon Help), which gives short explanation of the buttons when the mouse pointer is positioned over them. By default balloon help is activated. Deactivation of the balloon help will only be effective for the current session of FINE™/Turbo. When FINE™/Turbo is closed and launched again the balloon help will always be active by default. Furthermore, the section allows the user to control the Number of curves that can be plotted in the Convergence History page of the Task Manager. By default the parameter is set to 10 meaning that only 9 curves can be plotted in the steering (more details in Chapter 12). c) Solver Preferences In this section, the user may select the calculation accuracy for the flow solver. Single and double precision modes of the FINE™/Turbo solver are available. For most cases, the single precision solver (much less demanding in memory consumption) will be sufficiently accurate and should be considered as the default option. However, some special cases, such as very long thin pipe and conjugate heat transfer problems, may benefit from the double precision solver. One of the most important criteriums to choose the double precision solver is the maximum dimension of the domain and its positioning in the 3D field. If the ratio Δx ⁄ x local is bigger than roughly 1e-6, the double precision solver should be considered. Where Δx is the local cell size and x local is the local coordinate value. After selecting single or double precision solver, the value will be used as default value for new projects. 2-3.1.7 Quit Select the File/Quit menu item to quit the FINE™/Turbo integrated environment after confirmation from the user. The active project will be saved automatically by default (Save Active Project activated). Note that this action will not stop the running calculations. A FINE TaskManager window will remain open for each running computation. Closing the FINE TaskManager window(s) will kill the running calculation(s) after confirmation from the user. 2-3.2 Mesh Menu 2-3.2.1 View On/Off This toggle menu is used to visualize the grid in FINE™/Turbo GUI. It may take few seconds to load the mesh file for the first time. The parameters area will be overlapped by the graphic window, and the small control button on the upper - left corner of the graphic window can be used to resize the graphics area in order to visualize simultaneously the parameters and the mesh (see section 2- FINE™/Turbo 2-9 Graphical User Interface Main Menu Bar 6.6). Once the mesh is opened, the same menu item Mesh/View On/Off will hide it. Note that the mesh will stay in the memory and the following use of the menu will visualize it much faster than the first time. When the mesh is loaded the following items appear in the FINE™/Turbo interface: • the View subpad (see section 2-6.3 for more details), • the mesh information area (see section 2-6.4 for more details), • the graphics area will appear in the FINE™/Turbo interface (see section 2-6.6 for more details), • the Viewing buttons will appear on the bottom of the graphics area. Their function is described in section 2-6.7). The graphics area and the Viewing buttons will disappear when the mesh is hidden (Mesh/View On/Off). All the tools will disappear when the mesh is unloaded (Mesh/Unload). 2-3.2.2 Repetition This menu opens the following dialog box to control the repetition of the blocks when the mesh is visualized: For each block, the number of repetition desired can be set in the Nb Repet entry. The repetition of all blocks can be displayed or hidden respectively by pressing the Show or Hide button. 2-3.2.3 Tearoff graphics This menu transfers the graphics area and its control buttons into a separate window. Closing this window will display the graphics area back in the main FINE™/Turbo window. This feature is only available on UNIX systems. 2-3.2.4 Unload Mesh/Unload clears the mesh from the memory of the computer. 2-3.2.5 Properties Clicking on Mesh/Properties... opens a dialog box that displays global information about the mesh: • Grid Units: the user specifies the grid units when importing a mesh. When importing a mesh the Grid Units and Project Configuration window appears, which allows the user to check the mesh units (see section 2-2.3). The chosen units can be verified and, if necessary, changed. • Space Configuration: allows the user to verify whether the mesh is cylindrical or Cartesian and the dimensionality of the mesh. When importing a mesh the Grid Units and Project Configuration window allows the user to check these properties. Those chosen properties can be verified and, if necessary, changed. • The total number of blocks and the total number of points are automatically detected from the mesh. 2-10 FINE™/Turbo Main Menu Bar Graphical User Interface • For each block: the current (depending on the current grid level) and maximum number of points in each I, J and K directions, and the total number of points are automatically detected from the mesh. FIGURE 2.3.2-8 Mesh 2-3.3 Properties dialog box Solver Menu This menu gives access to the FINE™/Turbo solver, which is a powerful 3D code dedicated to Navier-Stokes or Euler computations. The FINE™/Turbo solver uses the computational parameters and boundary conditions set through the FINE™/Turbo GUI and can be fully controlled both from the FINE™/Turbo Solver Menu and from the Task Manager (see Chapter 11). In this section, the information is given on how to start, suspend, interrupt and restart the flow solver. All these actions may be simply performed by using the pull down menu appearing when the button Solver of the Menu bar is clicked. 2-3.3.1 Start Flow Solver To start the flow solver, select the menu item Solver/Start.... It is not recommended to start the flow solver before setting the physical boundary conditions and the computational parameters. Using the Start item to run the flow solver on active computation implies that the result file produced by a previous calculations on that computation will be overwritten with the new result values. It also implies that the initial solution will be created from the values set in the Initial Solution page. To restart a computation from an existing solution the solver should be also started using the Solver/Start... menu. On the Initial Solution page the initial solution has to be specified from an existing file (".run"). Chapter 9 describes the several available ways to define an initial solution. 2-3.3.2 Save To save an intermediate solution while the flow solver is running click on Solver/Save.... 2-3.3.3 Stop Flow Solver There are two different ways to stop the flow solver: • Solver/Suspend... interrupts the flow computation after the next iteration. This means that the flow solver stops the computation at the end of the next finest grid iteration and outputs the current state of the solution (solution files and CFView™ files) exactly as if the computation was finished. This operation may take from few seconds to few minutes depending on the FINE™/Turbo 2-11 Graphical User Interface Icon Bar number of grid points in the mesh. Indeed, if the finest grid is not yet reached, the flow solver continues the full multigrid stage and stops only after completion of the first iteration on the finest grid. • Solver/Kill... allows to stop immediately the computation for the active project. In this case no output is created and the only solution left is the last one that was output during the run. This may become a dangerous choice if asked during the output of the solution. The output is then ruined and all the computation time is lost. To avoid this, it is better to use Solver/Suspend... or to kill the computation some iterations after the writing operations. 2-3.4 Modules Menu Clicking on the menu item Modules shows a pull down menu with the available modules. The first four items are related to geometry and mesh definition: • IGG™ is the interactive geometry modeller and grid generator, • AutoGrid™ 4 & AutoGrid™ 5 are the automated grid generators for turbomachinery. • AutoBlade™ is the parametric blade modeller, Furthermore a design module is available: • Design3D is a product for three-dimensional blade analysis and optimization. The Task Manager is accessible with Modules/Task Manager. For more detailed information on the Task Manager consult Chapter 11. To start the flow visualization from FINE™/Turbo, click on the Modules/CFView ... and confirm to start a CFView™ session. Wait until the layout of CFView™ appears on the screen. CFView™ automatically loads the visualization file associated with the active computation. To visualize intermediate results of a computation, wait until the flow solver has written output. For more information about the flow visualization system, please refer to the CFView™ User Manual. Finally, the Harmo2Time module launches a reconstruction tool that will generate unsteady flow simulation results from existing harmonic flow simulation results, for more details, see Chapter 8-4. 2-4 Icon Bar The icon bar contains several buttons that provide a shortcut for menu items in the main menu bar. Also the icon bar contains a File Chooser to indicate the mesh linked to the project and a pull down menu to choose between Standard Mode and Expert Mode. 2-4.1 File Buttons The four buttons on the left of the icon bar are shortcuts for items of the File menu: The New Project icon is a shortcut for the menu item File/New. The Open Project icon is a shortcut for the menu item File/Open. 2-12 FINE™/Turbo Icon Bar Graphical User Interface The Save Project icon is a shortcut for the menu item File/Save. The Save RUN Files icon is a shortcut for the menu item File/Save Run Files. 2-4.2 Grid Selection Bar By clicking on the icon on the right of the bar a File Chooser is opened, which allows to select the grid file (with extension ".igg") of the mesh to use for the project. To select a grid not only the grid file with extension ".igg" needs to be present but at least the files with extensions ".igg", ".geom", ".bcs" and ".cgns" need to be available in the same directory with the same name as for the chosen mesh. If a mesh has already been linked to the current project and another mesh is opened, FINE™/Turbo will check the topological data in the project and compare it against the data in the mesh file. If the topological data is not equal, a new dialog box (Figure 2.4.2-9) will open. This dialog box informs the user that a merge of the topologies is necessary and will also show at which item the first difference was detected. The three following possibilities are available: • Merge Mesh Definition will merge the project and mesh data. For example, if a new block has been added to the mesh. The existing project parameters have been kept for the old blocks, and the default parameters have been set for the new block. • Open Another Grid File will open a File Chooser allowing to browse to the a new grid file with extension ".igg". Select the grid file and press OK to accept the selected mesh. Then the dialog box Mesh Merge Information will appear. • Start IGG will load automatically the new mesh into IGG™, where it can be modified. FIGURE 2.4.2-9 Merge Topology dialog box The merge process may also occur when opening an existing project, or when switching between IGG™ and FINE™/Turbo, because the check of the topology is performed each time when a project is read. FINE™/Turbo 2-13 Graphical User Interface Computation Management In case the mesh file no longer exists, or is not accessible, an appropriate warning will pop-up when opening the project. In this case it will not be possible to start the flow solver, so the user needs to locate the mesh by means of the File Chooser button on the right of the Grid Selection bar. Once the grid file is selected and its topology is checked, the Grid Units and Project Configuration window appears. This window allows to check the properties of the mesh and to modify them if necessary. See section 2-2.3 for more details on this window. 2-4.3 Solver Buttons Three buttons allow to start, suspend and kill the active computation: The Start Flow Solver icon is a shortcut for the menu item Solver/Start.... The Suspend Flow Solver icon is a shortcut for the menu item Solver/Suspend.... The Kill Flow Solver icon is a shortcut for the menu item Solver/Kill.... 2-4.4 Module Buttons Two buttons allow to start the pre- and post-processor: The Start IGG icon is a shortcut for the menu item Modules/IGG. The Start CFView icon is a shortcut for the menu item Modules/CFView. 2-4.5 User Mode By clicking on the arrow at the right the user may select the user mode. For most projects the available parameters in Standard Mode are sufficient. When selecting Expert Mode, parameters area included additional parameters. These expert parameters may be useful in some more complex projects. The next chapters contain sections in which the expert parameters are described for the advanced user. 2-5 Computation Management When selecting the Computations subpanel at the top left of the interface a list of all the computations in the project is shown. The active computation is highlighted in blue and the corresponding parameters are shown in the "parameters area". All the project parameters of the computation can be controlled separately by selecting (from this list) the computation on which all the user modifications are applied. 2-14 When selecting multiple computations, the parameters of the active page in the "parameters area" are copied from the first selected computation to all other computations. FINE™/Turbo Graphical Area Management Graphical User Interface With the buttons New Computation and Remove computations can be created or removed. When clicking on New Computation the active computation (highlighted in blue) is copied and the new computation has the same name as the original with the prefix "new_" as shown in the example below. In this example "computation_2" was the active computation at the moment of pressing the button New Computation. A new computation is created called "new_computation_2" that has the same project parameters as "computation_2". To rename the active computation click on Rename, type the new name and press . These options are also available when click-right on the active computation. Two buttons Create Performance Curve and Edit Performance Curve are dedicated to the creation and management of the performance curve for turbomachinary. More details can be found in Chapter 8-10. Right-Click FIGURE 2.5.0-10 Computations subpanel 2-6 Graphical Area Management 2-6.1 Configuration Management When creating a mesh within AutoGrid™ or IGG™, the multiblock data structure can become very complex. A database, named Grid Configuration, is created automatically at the end of the mesh generation, saved together with the project into a file ".config" (more details can be found in the IGG™ or AutoGrid™ User Manuals). To access the grid configuration menu in FINE™/Turbo, the Use Grid Configuration option has to be activated when linking the mesh for the first time, see section 2-2.3. This option is only available through a special license feature (SubProjects). FIGURE 2.6.1-11 Use FINE™/Turbo Grid Configuration 2-15 Graphical User Interface Graphical Area Management The grid configuration describes (as presented in the figure below) the mesh structure of the project as a tree through which the user can access the domain structure. The structure is defined as a set of fluid and solid domains interconnected together through domain interfaces. Each domain contains a set of subdomains and a set of interfaces. Each domain interface contains a type of boundary condition, a type of free boundary condition and the possible connected domain reference. FIGURE 2.6.1-12 Grid Configuration control This data structure is very useful. It can be used to reduce the time needed to analyse and visualize the mesh of a project, to setup the boundary conditions within FINE™/Turbo and to create subprojects starting from the main project (see Chapter 8 for more details). 2-6.2 Parameters Management The Parameters subpanel on the left, below the Computations subpanel, is presenting a directory structure allowing the user to go through the available pages of the project definition. The "parameters area" shows the parameters corresponding to the selected page in the parameters list. To see the pages in a directory double click on the name or click on the sign FIGURE 2.6.2-13 Parameters 2-6.3 in front of the name. subpanel View Area When the mesh is loaded with Mesh/View On/Off, a subpanel is shown in the list on the left: the View subpanel. By default the View subpanel is opened. It consists of three pages and controls the viewing operations on the geometry and the grid. The two first pages show the created geometry 2-16 FINE™/Turbo Graphical Area Management Graphical User Interface and/or block groups of the mesh and allow to create new groups. This possibility is only useful in the FINE™/Turbo GUI for visualization purposes (for example, to show only some blocks of the mesh to get a clearer picture in the case of a complex configuration). FIGURE 2.6.3-14 View subpanel The third page provides visualization commands on the grid. It consists of two rows: a row of buttons and a row of icons. The row of buttons is used to determine the viewing scope, that is the grid scope on which the viewing commands provided by the icons of the second row will apply. There are five modes determining the scope, each one being represented by a button: Segment, Edge, Face, Block, Grid. Only one mode is active at a time and the current mode is highlighted in yellow. Simply click-left on a button to select the desired mode. • : in Segment mode, a viewing operation applies to the active segment only. • : in Edge mode, a viewing operation applies to the active edge only. • : in Face mode, a viewing operation applies to the active face only. • : in Block mode, a viewing operation applies to the active block only. • : in Grid mode, a viewing operation applies to all the blocks of the grid. The icons of the second row and their related commands are listed in the following table: Icon Command Toggles vertices. Toggles fixed points. Toggles segment grid points. Toggles edges. FINE™/Turbo 2-17 Graphical User Interface Icon Graphical Area Management Command Toggles face grid. Toggles shading. 2-6.4 The display of vertices should be avoided since it allows to modify interactively in the graphics area the location of the vertices and therefore alter the mesh. The graphics area is for display purposes only and any modification on the mesh in the graphics area will not be saved in the mesh files and therefore not used by the flow solver. Mesh Information When the mesh is loaded also the Mesh Information area is shown containing the following information for the selected section of the mesh: Active block, face, edge and segment indices Number of blocks, faces, edges and segments for the active topology FIGURE 2.6.4-15 Mesh Information area • Active Block, Face, Edge and Segment indices. • Number of grid blocks, active block faces, active face edges, active edge segments. • Block: — Number of active block points. — Number of grid points. — Name of the block. — Number of points in each block direction. • Face: constant direction and the corresponding index. • Edge: constant direction according to the active face and the corresponding index. • Segment: number of points on the segment. 2-6.5 Parameters Area The Parameters area displays a page containing the parameters related to the selected item of the parameters list. Depending on the selected User Mode the available expert parameters will be displayed. 2-18 FINE™/Turbo Graphical Area Management 2-6.6 Graphical User Interface Graphics Area button to resize Graphics area FIGURE 2.6.6-16 Resizing of Graphics Area The graphics area shows the mesh of the open project. The graphics area appears and disappears when clicking on Mesh/View On/Off. When the graphics area appears it is covering the parameters area. Use the button on the left boundary of the graphics area to reduce its size and to display the parameters area. The Grid page, in the View subpanel on the left, and the viewing buttons can be used to influence the visualization of the mesh. The View subpanel is described in section 2-6.3 and the viewing buttons area are described below. 2-6.7 Viewing Buttons The viewing buttons are used to perform viewing manipulations on the active view, such as scrolling, zooming and rotating. The manipulations use the left, middle and right buttons of the mouse in different ways. The sub-sections below describe the function associated with each mouse button for each viewing button. For systems that only accept a mouse with two buttons, the middle mouse button can be emulated for viewing options by holding the key with the left mouse button. 2-6.7.1 X, Y, and Z Projection Buttons These buttons allow to view the graphics objects on X, Y or Z projection plane. Press the left mouse button to project the view on an X, Y or Z constant plane. If the same button is pressed more than one time, the horizontal axis changes direction at each click. FINE™/Turbo 2-19 Graphical User Interface Graphical Area Management 2-6.7.2 Coordinate Axes The coordinate axes button acts as a toggle to display different types of coordinate axes on the active view using the following mouse buttons: • Left: press to turn on/off the display of symbolic coordinate axis at the lower right corner of the view. • Middle: press to turn on/off the display of scaled coordinate axis for the active view. The axis surrounds all objects in the view and may not be visible when the view is zoomed in. • Right: press to turn on/off the display of IJK axis at the origin of the active block (in Block Viewing Scope) or of all the blocks (in Grid Viewing Scope). For more informations about the viewing scope, see section 2-6.3. 2-6.7.3 Scrolling This button is used to translate the contents of active view within the plane of graphics window in the direction specified by the user. Following functions can be performed with the mouse buttons: • Left: press and drag the left mouse button to indicate the translation direction. The translation is proportional to the mouse displacement. Release the button when finished. The translation magnitude is automatically calculated by measuring the distance between the initial clicked point and the current position of the cursor. • Middle: press and drag the middle mouse button to indicate the translation direction. The translation is continuous in the indicated direction. Release the button when finished. The translation speed is automatically calculated by measuring the distance between the initial clicked point and the current position of the cursor. 2-6.7.4 3D Viewing Button This button allows to perform viewing operations directly in the graphics area. Allowed operations are 3D rotation, scrolling and zooming. After having selected the option, move the mouse to the active view, then: • Press and drag the left mouse button to perform a 3D rotation • Press and drag the middle mouse button to perform a translation • Press and drag the middle mouse button while holding the key or use the mouse wheel to perform a zoom • To select the centre of rotation, hold the key and press the left mouse button on a geometry curve, a vertex or a surface (even if this one is visualized with a wireframe model). The centre of rotation is always located in the centre of the screen. So, when changing it, the model is moved according to its new value. The 3D viewing tool is also accessible with the key. 2-6.7.5 Rotate About X, Y or Z Axis The rotation buttons are used to rotate graphical objects on the active view around the X, Y or Z axis. The rotations are always performed around the centre of the active view. Following functions can be performed with the mouse buttons: • Left: press and drag the left mouse button to the left or to the right. A clockwise or counterclockwise rotation will be performed, proportional to the mouse displacement. Release the button when finished. 2-20 FINE™/Turbo Graphical Area Management Graphical User Interface • Middle: press and drag the middle mouse button to the left or to the right. A continuous rotation will be performed, clockwise or counter-clockwise. Release the button when finished. 2-6.7.6 Zoom In/Out This button is used for zooming operations on the active view. Zooming is always performed around the centre of the view. Following functions can be performed with the mouse buttons: • Left: press and drag the left mouse button to the left or to the right. A zoom in - zoom out will be performed, proportional to the mouse displacement. Release the button when finished. • Middle: press and drag the middle mouse button to the left or to the right. A continuous zoom in - zoom out will be performed. Release the button when finished. 2-6.7.7 Region Zoom This button allows to specify a rectangular area of the active view that will be fitted to the view dimensions. After having selected the button: 1. Move the mouse to the active view. 2. Press and drag the left mouse button to select the rectangular region. 3. Release the button to perform the zoom operation. These operations can be repeated several times to perform more zooming. Press or click the right mouse button to quit the option. The region zoom is also accessible with thekey. 2-6.7.8 Fit Button The fit button is used to fit the content of the view to the view limits without changing the current orientation of the camera (which can be interpreted as the user's eyes). 2-6.7.9 Original Button The original button is used to fit the content of the view and to change back to the default orientation of the camera. 2-6.7.10 Cutting Plane This option displays a movable plane that cuts the geometry and the blocks of the mesh. The plane is symbolically represented by four boundaries and its normal, and is by default semi-transparent. After having selected the button: • Press and drag the left mouse button to rotate the plane • Press and drag the middle mouse button to translate the plane • Press < x >, < y > or < z > to align the plane normal along the X, Y or Z axis • Press to revert the plane normal • Press < t > to toggle the transparency of the plane (to make it semi-transparent or fully transparent). It is highly advised to deactivate the plane transparency when using X11 driver to increase the execution speed. FINE™/Turbo 2-21 Graphical User Interface 2-7 Profile Management Profile Management When a law is defined by a profile clicking on the button invoke a Profile Manager window. FIGURE 2.7.0-17 Profile right next to the pull down menu will Manager for boundary conditions parameters The Profile Manager is used to interactively define and edit profiles for both fluids and boundary conditions parameters. The user simply enters the corresponding coordinates in the two columns on the left. The graph is updated after each coordinate (after each pressing of key). The button Import may be used if the profile exists already as a file on the disk. The Export button is used to store the current data in the profile manager as a file (for example to share profiles between different projects and users). The option Surface data allows the user to impose a 2D profile. The formats of the profile files are explained in Appendix A where all file formats used by FINE™/Turbo and the flow solver are detailed. If the mouse cursor is placed over a point in the graph window, this point is highlighted and the corresponding coordinates on the left will be also highlighted, giving the user the possibility to verify the profile. The button OK will store the profile values and return back to the main FINE™/Turbo window. 2-22 When imposing profiles, a zero extrapolation is applied for point located outside the defined range of the profile. E.g. if the density profile is given for a pressure between 10 bar and 100 bar, the density at 1 bar will be the one imposed at 10 bar. FINE™/Turbo CHAPTER 3: 3-1 Fluid Model Overview Every FINE™/Turbo project selects a fluid and its properties, defined by: 1. Using the fluid defined in the project file of which the properties are shown on the fluid selection page (see section 3-2.1), or 2. selecting a fluid from the fluid database included in the release that contains a set of pre-defined fluids (see section 3-2.2), or 3. creating a new fluid (see section 3-2.3). In the next section the interface is described in detail, including advises for use of the fluid definitions. The theoretical background for the different fluid models is described in the theoretical manual. FINE™/Turbo 3-1 Fluid Model The Fluid Model in the FINE™/Turbo GUI 3-2 The Fluid Model in the FINE™/Turbo GUI list of pre-defined fluids filters list of properties FIGURE 3.2.0-1 Fluid 3-2.1 Selection page Properties of Fluid Used in the Project Every FINE™/Turbo project contains a fluid with the corresponding properties that are displayed in the interface (see Figure 3.2.0-1). When a new project is created, the default fluid is a perfect gas, pre-defined by FINE™/Turbo. When an existing project is opened, the used fluid is defined by the properties as defined in the project file ".iec". The first listed fluid property is the fluid type. Four fluid types are available: • perfect gas, • real gas, • incompressible gas or liquid, • condensable fluid. For more details on each of these types, please see Chapter 2 in the theoretical manual. For the first three fluid types, the properties can be defined through the interface as described in section 3-2.3. To add a condensable fluid to the list of fluids proposed by default, please use TabGen to generate the appropriate tables. To modify the properties of the fluid used, a fluid can be selected from the list of pre-defined fluids (section 3-2.2) or a new fluid may be defined (where the new fluid is based on the current one, see section 3-2.3 for more detail). 3-2.2 List of Fluids The list of fluids (see Figure 3.2.0-1) contains pre-defined fluids in a database. For each fluid the fluid type and the permissions are defined. 3-2 FINE™/Turbo The Fluid Model in the FINE™/Turbo GUI Fluid Model Every fluid is associated with the user who created it and can be modified or removed only by its owner (the owner has Read Write Delete permissions). All other users will only have Read Only permissions. If the user selects a fluid from the list, the selection will be highlighted and the properties are displayed in the information box below the fluid list. Those fluid properties will be saved in the project file ".iec" as soon as the project is saved. 3-2.3 Add Fluid To add a fluid to the database click on the Add New Fluid... button. A new fluid is then created with the current properties as shown in the list of properties. A wizard will appear allowing the user to modify those properties. On the first page of this wizard the user can enter the name and the type of the new fluid. The name should be entered by moving the mouse to the text box for the Fluid Name and to type the name on the keyboard. By default a name is proposed like "new_fluid_1". The fluid type can be entered by selecting the appropriate check boxes. First make a choice for a compressible or incompressible fluid. For a compressible fluid select a perfect gas or a real gas. The fluid type corresponding to the selected checkboxes is shown in the text box for the Fluid Type. To cancel the modifications to the fluid definition and close the wizard click on the Cancel button. FIGURE 3.2.3-2 Fluid Wizard Once the fluid name and type are correctly set, click on Next>> to go to the next page of the wizard. On this page the following properties have to be defined: • Specific Heat Law, • Heat Conduction Law, • Viscosity Law, • Density Law (for an incompressible fluid only). The possible values to enter for these laws depend on the selected fluid type as described in the next paragraphs. In the case a law is defined by a constant value, type the value in the corresponding dialog box. In the case a law is defined by a profile, the Profile Manager can be opened by clicking on the button ( ) right next to the pull down menu (see section 3-2.3.6 for more detail). In the case a law is defined by a formula, the Formula Editor can be opened by clicking on the button ( next to the pull down menu (see section 3-2.3.5). FINE™/Turbo ) right Information linked to fluid creation is stored in the fluid database only when closing the FINE™/Turbo interface. As a consequence, this information will not be available to 3-3 Fluid Model The Fluid Model in the FINE™/Turbo GUI other users as long as this operation is not completed. 3-2.3.1 Definition of a Perfect Gas For the definition of a perfect gas the user has to specify: • The specific heat at constant pressure. For a perfect gas only a constant cp is allowed. • The constant specific heat ratio ( cp ⁄ cv ) characteristic of the fluid. • The heat conductivity which may be constant, defined by a polynomial or a profile in temperature or specified through a constant Prandtl number. • The viscosity law which may be constant, temperature dependent or specified by the Sutherland law. In case the viscosity depends on the temperature the user can specify the law through a polynomial or as a profile through the Profile Manager. Furthermore, when the viscosity law is defined by the Sutherland law, the Sutherland parameters are accessible by clicking on the button ( ) right next to the pull down menu. FIGURE 3.2.3-3 Sutherland Law Parameters The default law uses the dynamic viscosity but the user can specify the kinematic viscosity if required. 3-2.3.2 Definition of a Real Gas A real gas is defined by laws for the dependence of c p and/or gamma with the temperature and/or gas constant r. By default when adding a new fluid, the recommended specific heat law consists on imposing c p with the temperature and the gas constant r. The user can either define a profile, using the Profile Manager, or impose a polynomial approximation using the Formula Editor. In this last case, the polynomials take the following form: –3 + A1 T –3 + B1 T cp ( T ) = A0 T γ ( T ) = B0 T –2 + A2 T –1 + A3 + A4 T + A5 T + A6 T –2 + B2 T 1 –1 + B3 + B4 T + B5 T + B6 T 1 2 3 2 3 (3-1) (3-2) where the coefficients A 0, A 1, A 2, A 3, A 4, A 5, A 6, B 0, B 1, B 2, B 3, B 4, B 5 and B 6 are chosen by the user and set in the dialog box for c p and g respectively. In the definition of real gas properties, lower and upper bounds of temperature variations [Tmin-Tmax] allowed in the domain must be provided. 3-4 FINE™/Turbo The Fluid Model in the FINE™/Turbo GUI Fluid Model Depending on the local temperature during the iterative process, the physical properties will then be able to vary according to the laws defined in the fluid database. Note that it is necessary to cover the whole temperature range occurring in the system otherwise some inaccuracy in the results might be introduced. In addition, the local temperature may not fit at some occasion in the prescribed range; this is especially true during the transient. If so, as indicated by the formula editor (section 3-2.3.5), the physical properties are kept constant, at a value that corresponds to the lower/upper bound allowed by the range. FIGURE 3.2.3-4 New Fluid Definition - Real Gas For the default definition of a real gas, the user has to specify: • The gas constant r and the specific heat at constant pressure cp , which depend on the temperature through a polynomial or a profile. In both cases, the user has to specify the temperature range over which the specific heat is defined. Furthermore there are alternative modelling methods for a real gas that consists on: — involving a compressibility factor and two laws defining the dependence of cp and gamma with the temperature. — constant r model with gamma dependent on the temperature and cp calculated from r and gamma. For the pre-defined fluids, the value of c p is defined as a function of the temperature through a profile. These profiles have been computed for a constant pressure 100,000Pa. • The heat conductivity, which can be constant, defined by a polynomial or a profile in temperature or specified through a constant Prandtl number. • The viscosity law, which can be constant, dependent on temperature or specified by the Sutherland law. In case the viscosity depends on the temperature the user can specify the law through a polynomial or as profile. Furthermore, when the viscosity law is defined by the Sutherland law, the Sutherland parameters are accessible by clicking on the button ( ) right next to the pull down menu. The default law uses the dynamic viscosity but the user can specify the kinematic viscosity if required, see Figure 3.2.3-3. FINE™/Turbo 3-5 Fluid Model The Fluid Model in the FINE™/Turbo GUI Compared to a perfect gas computation ( c p and g constant), the real gas option results in an increase of about 25% of the CPU time. Real gas calculations are usually robust enough to avoid any use of a preliminary run with averaged physical properties. However, convergence difficulties may arise during the convergence process (say the first 100-200 iterations) if either the allowed temperature range is too large or if the properties are expected to vary significantly in the allowed temperature range. At these occasions, it is often useful to make an equivalent perfect gas computation, with average properties, in order to remove any temperature dependency and ease the convergence process. 3-2.3.3 Definition of a Liquid For the definition of a liquid two models are available: • a ’pure’ liquid with constant density, • a barotropic liquid for which the density varies with pressure. Depending on the type of liquid the user has to specify: • The specific heat at constant pressure. For liquids only a constant cp is allowed. • The heat conductivity, which can be constant, defined by a polynomial or a profile in temperature or specified through a constant Prandtl number. • The viscosity law, which can be constant, dependent on temperature or specified by the Sutherland law. In case the viscosity depends on the temperature the user can specify the law through a polynomial or as profile. Furthermore, when the viscosity law is defined by the Sutherland law, the Sutherland parameters are accessible by clicking on the button ( ) right next to the pull down menu. The default law concerned the dynamic viscosity but the user can specify the kinematic if required, see Figure 3.2.3-3. • The density law, which can be pressure dependent (using a polynomial law or as a profile through the Profile Manager) or following the Boussinesq law. In this latter case the density is constant and the Boussinesq coefficients are taken into account only if the button Gravity Forces (Flow Model page) is activated. These coefficients are used in source terms of the momentum equation and the energy equation in order to model the gravitational effect (i.e. natural convection) although the density is assumed to be strictly constant. For liquids, the reference temperature and pressure must lie in the expected range of the static temperature and pressure of the flow field. The reference pressure and temperature are defined on the Flow Model page (Eq. 4-19). 3-2.3.4 Definition of a Condensable Fluid The aim of the condensable fluid module is modelling the real thermodynamic properties of the fluid by means of interpolation of the variables from dedicated tables. A generation tool TabGen for the condensable tables is provided in FINE™/Turbo. The details can be found in Appendix D. The module can be used for a single-phase fluid of which the properties are too complex to be treated with a perfect or real gas model. It can also be used in order to treat thermodynamic conditions that are close to the saturation line. Note that the model can be used on the liquid or on the vapour side of the saturation curve. In case the thermodynamic state lies inside the two-phase region a homogeneous equilibrium two-phase mixture of vapour and liquid is considered. However the hypothesis of an equilibrium mixture is not valid if the dryness (wetness) fraction exceeds 20%. 3-6 FINE™/Turbo The Fluid Model in the FINE™/Turbo GUI Fluid Model The module can not be used above these fractions, as it completely ignores evaporation-condensation phenomena. The approach that has been adopted in the FINE™/Turbo solver consists of using a series of thermodynamic tables, one table being required each time a thermodynamic variable must be deduced from two other ones. This implies the creation of many tables as an input, but presents the advantage that no iterative inversion of the tables is done in the solver, with as a consequence a very small additional CPU time. By default, two sets of thermodynamic tables are provided in the standard FINE™/Turbo package: Refrigerant R134a and Water-Steam tables. The other thermodynamic tables can be generated using TabGen by the user or provided by NUMECA, upon request. In order to use a condensable gas as a fluid model, the user has to copy the provided tables in a userdefined subdirectory called "/tables_fluidname/". The location of this subdirectory is platform dependent: • On Unix/Linux systems: "/NUMECA_INSTALLATION_DIRECTORY/fine#/COMMON/thermodynamic_tables/" • On Windows systems: "/NUMECA_INSTALLATION_DIRECTORY/Fine#/bin/thermodynamic_tables/" The subdirectory has to be created before launching FINE™/Turbo. When the subdirectory is existing, the condensable gas is recognized by FINE™/Turbo and the fluid will appear in the list with respectively Fluid Name and Fluid Type as "Condensable__fluidname" and "Condensable Fluid". The condensable fluid option is not compatible with the use of cooling/bleed module and/or upwind schemes for space discretization. a) Selection of the Viscosity, Conductivity, and Specific Heat The viscosity and conductivity can be specified in two-dimensional tables. If it is not the case the other laws can be used (constant, polynomial expression or user profiles). Since the complete integration of the condensable fluid module in the user interface is not yet finished, the selection of these laws is no longer available as soon as a condensable fluid is chosen. The way to select these laws is the following: 1. create a perfect gas, 2. enter the desired properties for the viscosity and conductivity, 3. save the corresponding computation, 4. change the fluid type by selecting the condensable fluid. The same procedure applies to the specific heat at constant pressure, that is used in order to derive the turbulent conductivity from the turbulent viscosity. FINE™/Turbo 3-7 Fluid Model The Fluid Model in the FINE™/Turbo GUI 3-2.3.5 Formula Editor When a law is defined by a formula clicking on the button ( ) right next to the pull down menu will invoke a formula editor. When a law is defined by a formula clicking on the button right next to the pull down menu will invoke the Formula Editor. FIGURE 3.2.3-5 The Formula Editor for polynomials in the fluid properties The Formula Editor is used to define polynomial values for the fluid properties. The user has to define the seven coefficients of the polynomial according to the displayed formula on the top, and also the lower and upper limits of the temperature range, in which the polynomial function is defined. Press after each entry to validate the input. Values outside of the specified temperature range, will be considered constant and equal to the minimum or maximum value (as shown in the graph in Figure 3.2.3-5). If a fluid with "Read Only" permissions contains formulas they may be visualized by means of the Show Fluid Properties... button that opens the Formula Editor window, but they can not be modified - a message will warn the user that the selected fluid can not be modified. 3-2.3.6 Profile Manager When a law is defined by a profile clicking on the button ( the Profile Manager. ) next to the pull down menu will start The Profile Manager is used to interactively define and edit profiles for both fluid and boundary condition parameters. To input a profile, the user has to enter the corresponding coordinates in the two columns on the left. The graph is updated after each coordinate entry (after pressing the key). The button Import can be used to import a profile, which is already existing as a data file on the disk. The Export button is used to store the current data in the profile manager as a data file (for example to share profiles between different projects and users). The format of the profile files is explained in detail in Appendix A. If the mouse cursor is placed over a point in the graph window, this point is highlighted and the corresponding coordinates on the left will be also highlighted, giving the user the possibility to verify the profile. 3-8 FINE™/Turbo The Fluid Model in the FINE™/Turbo GUI Fluid Model The button OK will store the profile values into the fluid definition. FIGURE 3.2.3-6 Profile 3-2.4 Manager for fluid parameters If a fluid with "Read Only" permissions contains profiles they may be visualized by means of the Show Fluid Properties... button that opens the Profile Manager window, but they can not be modified - a message will warn the user that the selected fluid can not be modified. Only uniform distributions should be entered in the Profile Manager. Non-uniform distributions will be converted to a uniform distribution by the FINE™/Turbo solver. Delete Fluid from List When the user has the permission to delete a fluid, the button Delete Fluid... allows to remove the selected fluid from the list of available fluids. 3-2.5 Information linked to fluid removal is stored in the fluid database only when closing the FINE™/Turbo interface. As a consequence, this information will not be available to other users until this operation is completed. A message will however warn users that the fluid properties have been modified (up to removal in the present situation) by the owner. Edit Fluid When the user has the write permission for a fluid, the properties of the selected fluid can be modified by clicking on Edit Fluid.... A wizard will appear allowing to modify the name, the type and the laws defining the selected fluid. The two pages of this wizard and the laws to define are described in detail in section 3-2.3. FINE™/Turbo Information linked to fluid edition is stored in the fluid database only when closing the FINE™/Turbo interface. As a consequence, this information will not be available to other users until this operation is completed. A message will however warn users that the fluid properties have been modified by the owner. 3-9 Fluid Model The Fluid Model in the FINE™/Turbo GUI 3-2.6 Show Fluid Properties When the user does not have the write permission (Read Only) for a fluid the Show Fluid Properties... button opens the wizard with the properties of the fluid. In this case it is not possible to modify any of the properties in the wizard but the user has access to visualize the properties including the defined profiles and formulae. 3-2.7 Filters On the Fluid Model page two filters are available to display only a limited amount of fluids out of the complete list of fluids. Select the owner(s) and fluid type(s) to display from the pull down menus to limit the list of fluids. Please notice that under Windows™ the fluid database is not owner-oriented. The database is stored locally and user defined fluids are accessible with full permissions to all Windows users. The filters are used only to browse the fluid list and not to change the current fluid associated to the active computation except if selected in the list by left-click on it. 3-2.8 Import Fluid Database When the user has is own fluid database, the Import Fluids Database... enables to load a user defined database through a File Chooser window to select the ".flb" file containing the properties of all the fluids. When loading an existing project and opening the Fluid Model page, please notice that FINE™/Turbo is automatically checking if the fluid is existing or not in the fluid database. If the fluid name is existing but the properties are different, a comparison window will invite the user to select the fluid to use (the default fluid in the database or the fluid defined in the project). If the fluid is not existing in the fluid database, no fluid will be selected but the fluid parameters defined in the project will be kept. 3-2.9 Expert Parameters In this section, the expert parameters which can be used in the definition of the fluid type can be found. This is only a summary to know directly the expert parameters related to the definition of a fluid. All expert parameters related to fluid definition are available in Expert Mode in the Control Variables page. For these expert parameters the default values only have to be changed in case the user has specific wishes concerning the fluid modelling. PRT(real): Allows to define the turbulent Prandtl number (default value = 1.0). CLIPCG(integer): The thermodynamic tables are generated in a given range of thermodynamic variables. When the thermodynamic variables are not in the given range, the expert parmeter CLIPCG can be used to control the computing method of the dependent thermodynamic variable. 0 (default): the dependent thermodynamic variable is extrapolated from the interior field. 1: a clipping value will be used for the dependent thermodynamic variable. 3-10 FINE™/Turbo CHAPTER 4: 4-1 Flow Model Overview The Flow Model page, as displayed in Figure 4.1.0-1, can be used in order to specify several characteristics of the flow: • the time configuration to define time dependence of the equations to solve, • the mathematical model to: — choose between viscous and non-viscous flow, — choose between laminar and turbulent flow, — activate gravity, — activate pre-conditioning for low speed flow • the characteristic scales defining the Reynolds number of the flow, • the reference values of the temperature and pressure in the flow. This chapter is organised in the following way: • section 4-2 describes the interface and best practice for the definition of the mathematical model and especially the available turbulence models, • section 4-3 provides details on the Reynolds number related information and reference values. The interface and best practice for unsteady computations will be described in Chapter 6, The interface and best practice for harmonic method will be described in Chapter 8, FINE™/Turbo 4-1 Flow Model Mathematical Model FIGURE 4.1.0-1 Flow Model page. 4-2 Mathematical Model 4-2.1 Euler When selecting Euler on the Flow Model page an inviscid calculation will be performed. In such a case all solid walls are considered as Euler walls and the (non-zero) velocity is tangential to the wall. Since the Reynolds number has no meaning for Euler calculations this number is not displayed when Euler flow is selected. 4-2.2 Laminar Navier-Stokes When selecting Laminar Navier-Stokes equations the only effect is on the thermodynamic property of the flow. The viscosity will be the laminar kinematic viscosity and thus does not contain any turbulent component. 4-2.3 Turbulent Navier-Stokes When selecting Turbulent Navier-Stokes equations, turbulence is taken into account depending on the chosen turbulence model. In FINE™/Turbo, several turbulence models are available: • Algebraic model (0-equation): — Baldwin-Lomax • 1-equation model: 4-2 FINE™/Turbo Mathematical Model Flow Model — Spalart-Allmaras — Spalart-Allmaras (Extended Wall Function) — SARC, see Chapter 4-2.4.2 — SARC (Extended Wall Function), see Chapter 4-2.4.2 • 2-equation models: — k-ε (Extended wall function) — k-ε (Standard wall function), see Chapter 4-2.4.2 — k-ε (Low Re Yang-Shih) — k-ε (Low Re Chien) — k-ε (Low Re Launder-Sharma) — Shear Stress Transport (SST) — SST (Extended wall function) — EARSM — EARSM (Extended wall function) — k-ω (Wilcox) • 4-equation model: — v2-f (code friendly) For the Baldwin-Lomax model, algebraic formula is used to compute the turbulent data and consequently no additional input is needed. For all the 1/2/4 equation(s) models, additional equation(s) are solved and consequently suitable initial and boundary conditions must be defined in the interface. The DES (Detached Eddy Simulations) model has been implemented in FINE™/Turbo. For more information, please contact your local support office. In the following sections, the parameters related to the turbulence models are described. a) Boundary Condition Inlet • Spalart-Allmaras: the value of the turbulent viscosity must be defined. It might be constant or varying in space and time. The user can specify the time or spatial variation through the profile manager. • k-ε models: the values of the turbulent quantities (k and ε) must be defined. They might be constant or varying in space and time. The user can specify the time or spatial variations through the profile manager. • k-ω, SST and EARSM models: the values of the turbulent quantities (k and ε) must be defined. They might be constant or varying in space and time. The user can specify the time or spatial variations through the profile manager. The value for ω is determined according to: ε ω = --------- , with β*=0.09 β∗ k (4-1) • v2-f model: the values of the turbulent quantities (k and ε) must be defined. They might be constant or varying in space and time. The user can specify the time or spatial variations through the profile manager. The value of v2 is deduced by assuming an isotropic turbulence. FINE™/Turbo 4-3 Flow Model Mathematical Model b) Initial Condition • Spalart-Allmaras: a constant initial value of the turbulent viscosity is defined through the expert parameter NUTFRE on the Control Variables page under the Expert Mode. • k-ε models: the initial values of the turbulent quantities (k and ε) are specified by the user if a constant or initial solution for turbomachinery is chosen. • k-ω, SST and EARSM models: the initial values of the turbulent quantities (k and ε) are specified by the user if a constant or initial solution for turbomachinery is chosen. The value for ω is determined according to Eq. 4-1. • v2-f model: the initial values of the turbulent quantities (k and ε) are specified by the user if a constant or initial solution for turbomachinery is chosen. The value of v2 is deduced assuming an isotropic turbulence. It is not recommended to use a previously computed solution with different turbulence model. For k-ε models, the Chien and the Launder-Sharma models belong to the same family (zero value of ε at the wall) while the standard and Yang-Shih model belong to a second family (non zero value of ε at the wall). Launching a restart from a previously computed solution is only allowed as long as the user sticks to the same family. 4-2.4 Expert Parameters for Turbulence Modelling 4-2.4.1 Interfaced Expert Parameters In expert mode additional parameters related to turbulence modelling are available when using the turbulence models with extended wall functions. For these turbulence models the wall type can be defined as smooth or rough: • For a smooth solid wall (default) only the Von Karman constant and Bo have to be specified (κ and B). • When selecting a rough solid wall two additional parameters have to be specified: the equivalent roughness height and the zero-displacement plane (k0 and d0). 4-2.4.2 Non-interfaced Expert Parameters All non-interfaced expert parameters related to the turbulence models are accessible on the Control Variables page by selecting the Expert Mode. Calculation of the wall distances All turbulence models need to compute the wall distances everywhere in the computed domain. It is a rather time consuming process so that they are saved in the ".cgns" mesh file at the beginning of the first computation. These values will be read and used for the next computations. If the mesh file is modified or saved again, they are erased and will be computed again. Different important expert parameter are used in the calculation of the wall distance. The default values are generally sufficient and they have to be changed only if a problem arises. NREPET(integer): allows to take into account the periodicity of the computed domain. At each point of the domain, the closest wall is not always in the computed domain if periodic boundary conditions are used. Consequently the domain is repeated beyond the periodic boundaries to compute correctly the wall distance (default value =1). 4-4 FINE™/Turbo Mathematical Model Flow Model NSUBM(integer): is the maximum number of subdomains a domain is split into. Its value is sufficiently high and it must be changed only if an error message informs the user to increase it (default value = 1000). NTUPTC(integer): is the number of patches whose sub-patches will be searched. In a very complex geometry, the value of this parameter can be increased if the calculation of the wall distances fail (default value = 100). The computed wall distances should be removed from the mesh first before relaunching a computation with a different value of NTUPTC. To remove the computed wall distances, you should open your mesh in IGG™ and simply save it again. RTOL(real): maximum angle allowed between two normals of a patch (default value = 1.8). When the value of IDISTN is 1, the value of RTOL has to be set as the default value (1.8). When problems occur during the wall distance calculation (wall distance not equal to 0 on the wall), it is recommended to increase the value of NTUPTC (and to reduce RTOL if the wall distance gradient is not smooth). Please keep in mind that increasing this value will slow down the computing of the wall distances. IDISTN(integer): algorithm for wall distance calculation: 0 : old algorithm 1: new algorithm 2 (default): review of new algrithm (advised for 64 bits platforms) Limiters for all of the turbulence models MAVRES(real): denoted here ζ . This parameter limits the variation of the turbulence variables for each Runge-Kutta stage. Denoting the new value of k or ε as q lowing restrictions are imposed when MAVRES > 0: q n+1 q = max ( q n+1 n+1 = min ( q n , EPS,ζq ) n+1 n+1 , the fol- (4-2) n , ( 2 – ζ )q ) (4-3) where EPS is an expert parameter with a small value, default 1E-28, also used to avoid possible divisions by zero. The restriction defined in Eq. 4-3 is not applied to the turbulent dissipation rate (ε) when this tends to increase, in order to avoid excessive values of the turbulent viscosity. If MAVRES = 0, only the restriction defined in Eq. 4-2 is applied (avoiding negative values) If MAVRES < 0, the restriction is: q FINE™/Turbo n+1 n+1 n (1 + ζ)(q –q ) n – q = --------------------------------------------n + 1 n q –q - 1 + ------------------------n q (4-4) 4-5 Flow Model Mathematical Model MAVREM(real): a similar system is applied to the multigrid corrections with the expert parameter MAVREM, denoted below as ζ : If MAVREM > 0: q n+1 n – q < ( 1 – ζ )q n If MAVREM = 0: restriction to positive values If MAVREM < 0: q MUCLIP(real): n+1 n+1 n (1 + ζ)(q –q ) n – q = --------------------------------------------n + 1 n q –q - 1 + ------------------------n q controls the maximum allowable value for the ratio MUT/MU in the flow field but not on boundary conditions (default value = 5000). KEGRID(integer): allows the use of a particular full multigrid strategy. The Baldwin-Lomax model is used on the coarse grids during the full multigrid stage and the k, ε, v2 and f initial solution is obtained from the Baldwin-Lomax model solution. This parameter is not used for the Spalart-Allmaras model. KEGRID corresponds to the last grid level on which the algebraic model is used. For example, if the computation is done with 4 levels of multigrid and KEGRID is equal to 2, the Baldwin-Lomax model is used on the 333 (or level 4), 222 (or level 3) and 111 (or level 2) and the k-ε computation is initiated when transferring to the finest grid. If KEGRID is set to 3, the k-ε computation will be initiated when transferring to 222. If KEGRID is greater than the number of multigrid levels, the computation will be started on the coarsest level with k-ε. Baldwin-Lomax IATFRZ(integer): control the interaction of the model with the multigrid system 0: apply the turbulence model on all grid levels, 1: freeze turbulence on coarser grids (default), 2: freeze turbulence on all grids (see ITFRZ and RESFRZ). ITFRZ(integer): freeze the turbulent viscosity field if the fine grid iteration exceeds ITFRZ (default value = 1000000). RESFRZ(integer): freeze the turbulent viscosity field if the fine grid residual is lower than RESFRZ (default value = -12). Spalart-Allmaras NUTFRE(real): constant to initialize the turbulent viscosity field (default value = 0.0003). ITURRC(integer): the Spalart-Allmaras turbulence model with/without extended wall function does not take the rotation and curvature effects into account. Modifications have been brought in order to consider these effects. The modified Spalart-Allmaras model is marked as SARC model. 0(default): use the Spalart-Allmaras model, which does not take the rotation/ curvature effects into account. 2: use the SARC model, which takes the rotation/curvature effects into account. 4-6 FINE™/Turbo Mathematical Model Flow Model k-ε models CMU(real): constant for the k-ε model (default value = 0.09). CE1(real): constant for the k-ε model (default value = 1.44 automatically set to 1.35 for the Chien k-ε model). CE2(real): constant for the k-ε model (default value = 1.92 automatically set to 1.8 for the Chien k-ε model). SIGK(real): constant for the k-ε model (default value = 1.). SIGE(real): constant for the k-ε model (default value = 1.3). PRT(real): constant for the k-ε model - the turbulent Prandtl Number (default value = 1.). INEWKE(integer):allows the user to activate the k-ε (Standard wall function) model when the k-ε (Extended wall function) model is selected in the interface: 0: activate the the k-ε (Standard wall function) model. 10 (default): use the k-ε (Extended wall function) model. LTMAX(real): maximum turbulent length scale (default = 1.E+6), -1: control of turbulent length scale with automatic clipping. IYAP(integer): 1: applies the Yap’s modification to control the turbulent length scale. 0 (default): The value of the expert parameter LTMAX must be the default value. TEDAMP(real): parameter to improve the robustness of the k-ε models (default value = -1), > 0: a minimum of TEDAMP multiplication factor of the clipping value (EKCLIP) is used for k in the factor 1 ⁄ T ; a minimum of TEDAMP multiplication factor of the clipping value (EPCLIP) is used for ε to compute the turbulent viscosity, <= 0: the minimum values used for k and ε correspond to the expert parameter EPS, PRCLIP(real): sets an upper bound for the ratio between production and dissipation (default value = 50). LIPROD(integer): corresponds to a linearization of the production term (default = 1) when strain rate is large (i.e. impinging flow) and PRCLIP has no effect anymore on the flow field. EKCLIP(real): clipping value for the turbulent kinetic energy k (default value = 1.E-5). EPCLIP(real): clipping value for the turbulent dissipation rate ε (default value = 1E-5). IUPWTE(integer): uses an upwind scheme for the convection of k-ε instead of a centre scheme (default = 1). IKENC(integer): solves the k-ε equations with a non-conservative approach (default = 1). IKELED(integer): (= 1) activates the LED scalar scheme for k-ε instead of the standard central scheme (default = 0). IOPTKE(integer): optimized implementation for k-ε (Yang-Shih, Wall function, Lauder Sharma) (default = 1). FINE™/Turbo 4-7 Flow Model Mathematical Model All the above mentioned limiters are very important for the robustness of k-ε computations. With the exception of the length scale LTMAX all limiters are given appropriate defaults and it is not recommend to modify them. v2-f model CMUV2F(real): constant for the v2-f model (default value = 0.22), C1F(real): constant for the v2-f model (default value = 1.4), C2F(real): constant for the v2-f model (default value = 0.3), CL(real): constant for the v2-f model (default value = 0.23), CET(real): constant for the v2-f model (default value = 70.0), CE2V2F(real): constant for the v2-f model (default value = 1.9), SIGE(real): constant for the v2-f model (default value = 1.3), SIGK(real): constant for the v2-f model (default value = 1), EKCLIP(real): clipping value for the turbulent kinetic energy k (default value = 1.E-5), EPCLIP(real): clipping value for the turbulent dissipation rate ε (default value = 1E-5), k-ω (Wilcox) The parameters for the k-ω (Wilcox) model are hard coded. The user cannot modify the default values. Shear Stress Transport (SST) GAM1(real): constant for the SST model (default value = 0.5532), GAM2(real): constant for the SST model (default value = 0.4403), BETA1(real): constant for the SST model (default value = 0.075), BETA2(real): constant for the SST model (default value = 0.0828), SICK1(real): constant for the SST model (default value = 0.85), SICK2(real): constant for the SST model (default value = 1.0), SIGO1(real): constant for the SST model (default value = 0.5), SIGO2(real): constant for the SST model (default value = 0.856), A1SST(real): constant for the SST model (default value = 0.31), BETSST(real): constant for the SST model (default value = 0.09). EARSM 4-8 GAM1(real): constant for the EARSM model (default value = 0.5532), GAM2(real): constant for the EARSM model (default value = 0.4403), BETA1(real): constant for the EARSM model (default value = 0.075), FINE™/Turbo Mathematical Model Flow Model BETA2(real): constant for the EARSM model (default value = 0.0828), SICK1(real): constant for the EARSM model (default value = 0.5), SICK2(real): constant for the EARSM model (default value = 1.0), SIGO1(real): constant for the EARSM model (default value = 0.5), SIGO2(real): constant for the EARSM model (default value = 0.856), A1SST(real): constant for the EARSM model (default value = 1.245), BETSST(real): constant for the EARSM model (default value = 0.09). 4-2.5 Best Practice for Turbulence Modelling 4-2.5.1 Introduction to Turbulence Turbulence can be defined as the appearance of non-deterministic fluctuations of all variables (velocity u', pressure p', etc...) around mean values. Turbulence is generated above a critical Reynolds number that may range in values from 400 to 2000 depending on the specific case. In 95% of industrial applications the critical Reynolds number falls above that range. That is why it is in general necessary to predict adequately the turbulence effects on the flow-field behaviour. To model turbulent flow in a satisfactory way, four steps should be performed: • choosing a turbulence model, • generating an appropriate grid, • defining initial and boundary conditions, • if necessary, setting expert parameters to procure convergence. 4-2.5.2 First Step: Choosing a Turbulence Model. A turbulence model is chosen based on the specific application. Table 4-1 states the most appropriate turbulence models to use for different types of flows. Although these are the "most appropriate" this does not mean that certain turbulence models cannot be used for the flow types listed, but just that they are "less appropriate". According to the method accounting for viscous effects close to the wall, the turbulence models can be divided into two types: high Reynolds number turbulence models and low Reynolds number turbulence models. Please note that here "high Reynolds number" and "low Reynolds number" refer to the local turbulent Reynolds number Re l = u'l ⁄ ν formed by the turbulent fluctuation u' , turbulent length scale l and kinematic viscosity ν . The high Reynolds number turbulence models assume that the flow near the wall behaves like a fully developed turbulent boundary layer and prescribe boundary conditions by employing wall functions. The viscous sublayer will not be resolved. In FINE™/Turbo, both standard wall function and extended wall function are available, see the theoretical manual for the detailed information. The low Reynolds number turbulence models resolve the entire boundary layer, including the viscous sublayer where the viscous diffusion is much larger that the turbulent one. Thus, sufficiently fine grid should be used inside the boundary layer so that the sharp gradients can be resolved. FINE™/Turbo 4-9 Flow Model Mathematical Model High-Re: Low-Re: Turbulence Models Spalart-Allmaras (Extended Wall Function); SARC (Extended Wall Function); k-ε (Extended wall function); k-ε (Standard wall function); SST (Extended wall function) EARSM (Extended wall function); Baldwin-Lomax; Spalart-Allmaras; Spalart-Allmaras (Extended Wall Function); SARC; SARC (Extended Wall Function); k-ε (Extended wall function); k-ε (Low Re Yang-Shih); k-ε (Low Re Chien); k-ε (Low Re Launder-Sharma); Shear Stress Transport (SST); SST (Extended wall function); EARSM; EARSM (Extended wall function); k-ω (Wilcox); v2-f (code friendly) Most Appropriate Flows Quasi-2D; Weak pressure gradient; Quick design-cycle calculations 3D; Strong pressure gradient; Moderate curvature; Separating flows TABLE 4-1 Recommended turbulence models for different flow types Three main kinds of turbulence models exist: • algebraic models (e.g. Baldwin-Lomax), • one-equation models (e.g. Spalart-Allmaras), • two (four)-equation models (k-ε, k-ω and v2-f). When quick turbulence calculations are required, for example, in design-cycle analysis, it is recommended that the Baldwin-Lomax model is used due to its high numerical stability and low computational expense. To simulate more precisely the turbulent quantities with also a good rate of convergence the Spalart-Allmaras model should be preferred. Another model often used in design is the "standard" k-ε model. This model employs an empirically based logarithmic function to represent the near-wall physics and requires a lower grid resolution in this region as a result. One drawback of this treatment is that the logarithmic function does not apply for separated flows, although the NUMECA extended wall function will still work. If it is expected that a significant amount of separation will have to be predicted, one of the low-Reynolds number turbulence models would be more appropriate. All of the listed turbulence models employ constant turbulent Prandtl numbers which is somewhat of a restriction when performing heat transfer calculations. However, experience has shown quite successful prediction of heat transfer coefficients when using low Reynolds models. The Shear Stress Transport (SST) k-ω turbulence model is another most utilized two-equation model. This model, which combines the advantages of the Wilcox k-ω model and the k-ε model, has higher accuracy in the separation flow predictions. The user is recommended to use the SST kω model in predicting the onset and the amount of separations under adverse pressure gradient conditions. The EARSM (Explicit Algebraic Reynolds Stress Model) model is a non linear eddy viscosity 2equation model. EARSM is much less demanding than RSM from the computational standpoint and, at the same time, is capable of reproducing some important features of turbulence (e.g. its ani- 4-10 FINE™/Turbo Mathematical Model Flow Model sotropy in the normal stresses), which are beyond the capabilities of linear eddy viscosity turbulence models. The user is recommended to use the EARSM model when strong anisotropy exists in the computational domain. The v2-f turbulence model was developed to eliminate the need to the damping functions that used by the low-Reynolds k-ε turbulence models. Through several years of fundamental research, v2-f turbulence model has been proven to have better behavior in predicting wall induced phenomena such as heat transfer and flow separation than the other low-Reynolds turbulence models. The user is suggested to use this model in heat transfer applications. The v2-f turbulence model has not been extended to some specific modules: Rotor/ Stator interfaces, Full Non-Matching connections and Cooling/Bleed module. 4-2.5.3 Second Step: Generating an Appropriate Grid. a) Cell Size When calculating turbulence quantities it is important to place the first grid node off the wall within a certain range (ywall). This can be done for the blade and the endwalls (hub and shroud) independently. When doing computations including viscosity (Navier-Stokes equations) the boundary layer near a solid wall presents high gradients. To properly capture those high gradients in a numerical simulation it is important to have a sufficient amount of grid points inside the boundary layer. When Euler computations are performed no boundary layer exists and therefore the cell size near solid walls is of less importance. To estimate an appropriate cell size ywall for Navier-Stokes simulations including turbulence, the local Reynolds number based on the wall variable y+ is computed. The value of y+ associated with the first node off the wall will be referred to here as y1+: ρu τ y wall y1+ = -------------------- μ (4-5) where uτ is the friction velocity: uτ = τ wall ----------= ρ 1--( V )2 Cf 2 ref (4-6) Note that the value of ywall depends on the value of y1+. FINE™/Turbo 4-11 Flow Model Mathematical Model viscous sub-layer buffer layer log layer defect layer Separating flow logarithmic law Data of Lindgren (1965) Note that the sublayer extends up to y+=5 but 10 is an acceptable approximation for design calculations. Note: The variable v* displayed in the figure is uτ. Picture from White, F.M., Viscous Fluid Flow, McGraw Hill, 1991. FIGURE 4.2.5-2 Boundary layer profiles In Figure 4.2.5-2 it is represented the evolution of u+ against y+ from the measurements of Lindgren(1965) with: u+= u / u τ Low-Re models resolve the viscous sublayer and are well suited for y1+ values less than 10 whereas high-Re models apply analytical functions to the log-layer and are appropriate to y1+ values ranging from 20 to 50, even more (depending on the extension of the buffer layer for the considered flow). When the extended wall function is used, it is strongly advised to locate the first inner node either in the viscous sublayer (y1+<5) or in the log layer (y1+>20). Moreover one can notice that the logarithmic function does not apply for separated flow. So whether it is expected that a significant amount of separation will have to be predicted, one of the low-Reynolds number turbulence models would be more appropriate. Recommendations are given in the table below for ranges of y1+ specific to the different types of models. 4-12 FINE™/Turbo Mathematical Model Flow Model High-Re: Low-Re: Turbulence Models Spalart-Allmaras (Extended Wall Function); SARC (Extended Wall Function); k-ε (Extended wall function); k-ε (Standard wall function); SST (Extended wall function) EARSM (Extended wall function); Baldwin-Lomax; Spalart-Allmaras; Spalart-Allmaras (Extended Wall Function); SARC; SARC (Extended Wall Function); k-ε (Extended wall function); k-ε (Low Re Yang-Shih); k-ε (Low Re Chien); k-ε (Low Re Launder-Sharma); Shear Stress Transport (SST); SST (Extended wall function); EARSM; EARSM (Extended wall function); k-ω (Wilcox); v2-f (code friendly) y1+ 20-50 <10 TABLE 4-1 Appropriate y1+ values for available turbulence models One way to estimate ywall as a function of a desired y1+ value is to use a truncated series solution of the Blasius equation: V ref – 7 / 8 L ref 1 / 8 --------y wall = 6 --------- y1+... 2 ν (4-7) Note that the reference velocity, Vref, can be taken from an average at the inlet. For instance, if the mass flow is known the value can be calculated using density and the cross-sectional area of the inlet. If the mass flow is not known the reference velocity may be calculated from the inlet total pressure and an estimated static pressure using isentropic relations. The reference length, Lref, should be based on a typical length scale since an estimation of boundary layer thickness is implied in this calculation. For instance, in the case of a turbomachinery simulation one could use the distance between hub and shroud curves that exist upstream of the first row of blades. This is approximate, of course, as the thickness of the boundary layers will vary widely within the computational domain. Fortunately it is only necessary to place y1+ within a range and not at a specific value. Another method of estimating ywall is to apply the 1/7th velocity profile. In this case the skin friction coefficient Cf is related to the Reynolds number: 0.027C f = ------------Re x1 / 7 (4-8) where Rex should be based on average streamwise values of Vref and Lref as discussed above. Since uτ is based on Cf it may be calculated based on Eq. 4-6, and ywall may then be calculated from Eq. 4-5. Note that either method is not exact but they will yield results that are quite close to each other. In fact, it can be instructive to calculate ywall using both methods as a check. Since only one wall distance is being calculated, the particular flow being studied should be kept in mind. For instance if it is a diffusing flow Cf, and hence y1+, can be expected to drop. Since a certain range is desired (e.g., 20< y1+<50 for high-Re Standard k- ε) the user may choose to base the calculation of wall distance on an average of that range (e.g., 40). FINE™/Turbo 4-13 Flow Model Mathematical Model b) Things to Look Out For Previous recommendations should provide reasonable estimates but it is always wise to plot y+ once a solution has finished. Spot checks should be made to ensure that most y1+ values fall within the desired range. For instance it is useful to plot y+ contours over the first layer of nodes from a given wall (available in solid data output, see section 10-2.1.5). There are some special cases where such checks do not strictly apply. For instance, skin friction approaches zero at points of separation so it is expected that y1+ will be low in such regions. It is generally recommended that turbomachinery blade tip clearances are meshed with uniform spanwise node distributions. In such cases, the y1+ values will tend to be higher within the gap than elsewhere in the computational domain nearwall regions. This should not raise concern as the tip clearance flow consists of thoroughly sheared vortical fluid that undergoes significant acceleration and is therefore quite different than a standard boundary layer. It is expected that the skin friction will be high in this region due to the acceleration. c) General Advice • What grid resolution is adequate? The resolution method employed in the FINE™/Turbo solver requires approximately 9 nodes across a free shear-layer and approximately 15 across a boundary layer to provide grid-independent results for turbulent flows. If wall functions are used the boundary layer only requires approximately 9 nodes. Of course the flow field under study will realistically consist of shear layers of which the width varies substantially throughout the flow field. The user must therefore decide what is important to capture and what is not. For instance, in the design-cycle analysis of a compressor with a volute it would probably be acceptable to choose a fully-developed boundary layer. The number of nodes across the diameter would therefore be approximately 29. However, it would be wise to select a number like 33 to maintain a large number of multi-grid levels. The selection of nodes in the streamwise direction should be governed by what resolution adequately represents the studied geometry. Regions of concentrated high gradients, such as airfoil leading or trailing edges or any geometrical corners should contain a relatively high clustering of nodes. • What determines the grid quality? After the various grid resolution concerns are addressed, the level of skewness must be analysed. Providing clustering in a curved geometry can often lead to internal angles of grids cells of 10o. It is important to minimize the number of cells containing such low angles as the calculation of fluxes can become significantly erroneous under such conditions. More information concerning how to check the quality of a grid can be found in the IGG™ or AutoGrid™ manual. If the adjustment of node numbers and clustering does not reduce the level of skewness, local smoothing should be applied. The expansion ratio, or the ratio of adjacent cell sizes, should also be checked. It is particularly important to keep this value within an absolute range of about 1.0-1.6 in regions of high gradients, such as boundary layers, free shear-layers and shocks. If it is evident that adjacent cells are different in size by factors significantly greater than two, the clustering in this region should be reduced or the number of nodes should be increased. d) Verification of y1+ By following these instructions it should be possible to generate a grid of reasonable quality for turbulent flows. It is recommended however, that the user checks values of y1+ after approximately one hundred iterations on the fine grid to ensure the proper range has been specified. At the same time, it can be useful to plot contours of residuals (continuity, momentum, energy and turbulence) 4-14 FINE™/Turbo Mathematical Model Flow Model over selective planes. If the level of skewness is too high, this will be indicated by local peaks in residuals that are orders of magnitude greater than the rest of the flow field. If a multi-block grid is used, the residual levels in each block can be compared in the Monitor. 4-2.5.4 Defining Initial & Boundary Conditions Turbulence is commonly modelled by emulating molecular diffusion with a so-called "eddy-viscosity" (μT). A standard method for determining μT is based on turbulent-eddy length and time scales that are modelled through turbulence kinetic energy (k) and dissipation (e.g. ε) equations. It is important to note that the level of turbulence quantities (i.e. turbulence intensity, μT, k, ε) specified at the inlet boundary can have a strong effect on the flow-field prediction for quantities like the total pressure, velocity profiles, flow angles, total temperature etc. Since the measurement of turbulence is rarely conducted in a design and test environment, the designer faces the problem of setting these quantities without knowing the correct values. a) Spalart-Allmaras Model When the Spalart-Allmaras model is selected, the kinematic turbulent viscosity νt (m2/s) has to be specified. The kinematic turbulent viscosity ratio is extremely sensitive to the type of application/ configuration. Therefore, if the user has any indication of the actual level of turbulence in the case configuration, the user should use it. If no information is available on the order of magnitude of the kinematic turbulent viscosity ratio, estimates can be made based on the following assumptions that: ν ν • For internal flows (e.g. turbomachinery): ----t = 1 to 5. ν ν • For external flows (e.g. vehicle aerodynamics): ----t = 1 . b) k-ε, k-ω, EARSM and v2-f Models When the k-ε, k-ω and v2-f models are selected, the boundary values of k and ε have to be specified. If no information is available on the turbulence properties of the flow, estimates can be made based on the following formulations. b.1) Estimation of k The value of the turbulent kinetic energy k can be derived from the turbulence intensity Tu or from the wall shear stress. — From the turbulence intensity: The turbulence intensity Tu can be expressed against the streamwise fluctuating velocity u' and the streamwise velocity Uref: 2 u' T u = ---------U ref (4-9) For internal flows the value of Tu is about 5% and for external flows it is reduced to 1%. With these considerations k can be calculated in considering an isotropic turbulence: 2 3 k = --- u' 2 2 (4-10) — From the wall shear stress: If the wall shear stress is known, the user can use the wall functions defined for the fully turbulent flow: FINE™/Turbo 4-15 Flow Model Mathematical Model τ wall k = ----------ρ Cμ (4-11) This value of k could be used as an initial value and also for the inlet boundary condition. b.2) Estimation of ε The value of the turbulent dissipation can be specified through one of the following rules: — Specify the ratio of the turbulent viscosity to the laminar viscosity: 2 μ ρ ref k ε = C μ ---- ------------μt μ (4-12) For internal flows (such as turbomachinery flow), typical values are μ t ⁄ μ = 50 . For external flows (in aerodynamics computations), typical values are μ t ⁄ μ = 1 . — Specify the turbulent length scale (only for internal flows): A typical values is l = 0.1D H . where DH is the hydraulic diameter of the inlet section 3 3 --- --4 2 cμk ε = ---------l (4-13) — Derive ε from the asymptotic turbulent kinetic equation: In a free uniform flow the turbulent kinetic energy equation reduces to ∂k u ----- = – ε ∂x (4-14) This relation can be used to specify the value of the turbulent dissipation in the following way: Δk ε = – u -----L (4-15) where u is the inlet velocity, Δk the decay of the turbulent kinetic energy over a length L. For example, in a turbomachine, L is the maximum geometric length and Δk could be set to 10% of the inlet value of k. Using this method, the user must make sure that the value of the turbulent viscosity obtained μ μ from these values of k and ε is not too big or too small. i.e. 1 < ----t < 1000 . If this condition is not satisfied, it is advised to scale down or up the value of k inlet or the Δk and compute again the turbulent dissipation — Specify the wall shear stress: If the wall shear stress is known, the user can use the wall functions defined for the fully turbulent flow. 3 --2 ( τ wall ⁄ ρ ) ε = -----------------------l (4-16) If there is an initial solution file containing k and ε , the k and ε values of this file are used to initialize the fields. 4-16 FINE™/Turbo Mathematical Model Flow Model The values of the inlet boundary conditions for the k and ε can also be used to set the initial k and ε fields. However, to reduce the possibility of oscillations in skin friction due to non-physical relaminarisation during convergence, it is recommended to insure ε ≈ 0.1 ε inlet . Either of the above methods can be applied for setting the boundary conditions in turbomachine applications. However, if the given values of k and ε lead to the damping of the turbulence shortly after the inlet section, we suggest to apply Eq. 4-15 and select an inlet values of k such that the ratio of the turbulent viscosity to the laminar viscosity equals 50. In some cases a cross-check between Eq. 4-12 and Eq. 4-14 may result in very different values for ε. In such a case it is recommended to re-evaluate k and ε in the following manner: 1. Use relation Eq. 4-15: Δk 0.1k ε = – u ------- = u ---------ΔL ΔL (4-17) This relation expresses that k0 (k at the inlet) is expected to be decreased by about 10% over a length ΔL that is characteristic to the size of the domain. 2. Use relation Eq. 4-12. In this relation Cμ=0.09 and μ represents the dynamic laminar viscosity of the fluid. 3. Combine the relations of the two previous steps to remove ε0, leading to: 0.1U μ t ν k 0 = ------------ ---- ------ ΔL μ C μ 4. (4-18) Using either relation Eq. 4-12 or Eq. 4-15 then easily leads to an estimation of ε0. 4-2.5.5 Setting Expert Parameters to Procure Convergence Several expert parameters may be set to procure convergence. a) Cut-off (Clipping) of Minimum k Value The float parameter EKCLIP controls the minimum allowable value of k. This is done to prevent non-physical laminarisation and remove the possibility of negative values being calculated during numerical transients. Setting this value to a reasonable level has been shown to significantly increase the convergence rate. EKCLIP(real): clipping k to about 1% of inlet value maintains minimum residual turbulence in the domain. b) Minimizing Artificial Dissipation in the Boundary Layer An alternative treatment of the dissipation terms in the k and ε equations has been introduced to overcome difficulties related to turbulence decay in boundary layers observed in some specific test cases. Currently, the dissipation terms are scaled with the spectral radius of the equations and are further damped in an exponential manner across the boundary layer. The major drawback of this formulation is that it introduces an excessive amount of artificial dissipation into the boundary layer, leading to non-physical relaminarisation problems. A different implementation, based on the L.E.D. (Local Extrema Diminishing) version of the Jameson-Schmidt-Turkel treatment introduces better monotonicity properties of the k and ε equations. FINE™/Turbo 4-17 Flow Model Mathematical Model IKELED(integer): 0 (default): Dissipation scaled with spectral radius. 1: Less diffusive L.E.D. scheme activated. c) Wall Function for the k-ε Turbulence Model INEWKE(integer):0: Wall function applies for first node off the wall at y+ =20-50, Launder & Spalding. 10 (default): Mesh-independent formulation of the wall function. d) Full Multigrid k-ε / Baldwin-Lomax & v2-f / Baldwin-Lomax Switch KEGRID = 2(default) Grid 222 - Baldwin Lomax, Grid 111 - Baldwin Lomax, Grid 000 - k-ε or v2-f Model. KEGRID = 3: Grid 222 - Baldwin Lomax, Grid 111 - k-ε or v2-f Model, Grid 000 - k-ε or v2-f Model. Example: k-ε run on the finest grid level (000) with 3 levels of grid (222, 111 & 000) in the multigrid procedure. The Baldwin-Lomax model remains active on levels 222 and 111 before k-ε is automatically switched on when the finest grid is reached. This is controlled through the expert parameter KEGRID whose value is set to 2 by default, meaning that the Baldwin Lomax model is used up to the second level of grid. The μt / μ field computed using the Baldwin-Lomax model is then transferred to the finest mesh and used to calculate initial k and ε values. The use of a KEGRID value higher than the number of grid levels available enables the k and ε equations to be solved on all grid levels. A similar procedure can be followed when a calculation on 111 mesh is first desired. Providing KEGRID is set to 2 (default value), the Baldwin-Lomax is then active on level 222 before the k-ε model is automatically switched on when the finest grid level (111 in this case) is reached. However, the question then arises when a restart procedure on the 000 level is required. How to restart on 000 while transferring strictly the k and ε fields already computed on 111? By default, since KEGRID=2, the solution computed on 111 is seen as a Baldwin-Lomax solution. The k and ε fields are then reset using the classical procedure while the other variable fields (density, velocity and energy) are transferred adequately. To overcome this difficulty, KEGRID must again be set to a value higher than the number of grids. This procedure results in a much better initialisation of k and ε, thus preventing some relaminarisation while enhancing convergence. e) Cut-off (clipping) of Maximum Turbulence Production/Destruction Value The float parameter PRCLIP controls the maximum allowable value of turbulence production/ destruction (=production/density*dissipation in k-ε model). Limiting this to a finite value enhances the convergence rate by removing the possibility of unbounded turbulence spikes occurring during the numerical transient. However, care must be taken to apply a reasonable limit. Recommended values are: PRCLIP (real): For most flows: 50 (default), In turbulent diffusion dominated flows (e.g., seals): 200. 4-18 FINE™/Turbo Mathematical Model Flow Model f) Cut-off (clipping) of Maximum Turbulent Viscosity Ratio (μt /μ) The float parameter MUCLIP controls the maximum allowable value of the turbulent viscosity ratio μt/μ. Limiting this to a finite value enhances the convergence rate by removing the possibility of unbounded spikes occurring during the numerical transient. At the end of the computation however, the value of μt/μ should not be clipped anymore. During the convergence process, the user can check the output of the computation to see if the maximum value for the turbulence ratio has been reached. If this is the case, the output will contain a line: "MUT/MU CLIPPED FOR # CELLS". MUCLIP can then be put to a higher value, to increase the limit. However, care must be taken to apply reasonable limits. Recommended values are: MUCLIP (real): 4-2.6 For most flows: 5000 (default). It can be increased if necessary. Laminar-Transition Model 4-2.6.1 Introduction The boundary layer which develops on the surface of a solid body starts as a laminar layer but becomes turbulent over a relatively short distance known as the transition region. This LaminarTurbulent transition is a complex and not yet fully understood phenomenon. Among the numerous parameters that affect the transition one can list: the free stream turbulence intensity, the pressure gradient, the Reynolds number, and the surface curvature. Furthermore, predicting the onset of turbulence is a critical component of many engineering flows. It can have a tremendous impact on the overall drag, heat transfer, and performances especially for low-Reynolds number applications. However, most of the turbulent models fail to predict the transition location. Therefore, a laminar-transition model is proposed in the FINE™/Turbo solver in order to take into account the effect of the laminar-turbulent transition. The following four choices are possible in the Transition Model page under Optional Models: — — — — Fully Turbulent Fully Laminar Forced Transition Abu-Ghannam and Shaw (AGS) Model The present transition model can be used only with the low Reynolds number Spalart-Allmaras, Yang-Shih k-epsilon, Wilcox k-omega and SST turbulence models. The transition model in FINE™/Turbo is mainly devoted to turbomachinery applications using AutoGrid™ mesh. Both the pressure and suction sides of the blade need to be set with the transition model. Chapter 8-9 describes the interface for the transition model. More information on the transition model can be seen in Chapter 3-8 in the theoretical manual. However, the transition model in FINE™/Turbo is also available for the other cases, such as flat plate, wings and hydrofoils, etc. In the next section a best practice will be given to describe how to model transition on non-turbomachinery cases. 4-2.6.2 How to model transition on non-turbomachinery cases Use of the transition model is restricted to the pressure and suction sides of the turbomachinery blade using AutoGrid™ mesh. Modeling transition on non-turbomachinery cases can therefore only be performed by considering the object to be a pseudo "blade" and modifying the mesh files manually. The limitation on the mesh of non-turbomachinery cases is: FINE™/Turbo 4-19 Flow Model Mathematical Model • The mesh topology should be similar to a Autogrid™ mesh topology (with at least a proper mesh in spanwise direction). • The transition is along a pseudo "blade", so the user has to add the "blade" definition in the mesh files manually. Example: Mesh for modeling transition on a flat plate Considering transition flow over a flat plate (Figure 4.2.6-3). The computational domain corresponds to an external flow with a constant velocity blowing towards the flat plate. Note that for the flat plate case the user has to consider the two faces of the plate since the transition model needs a pressure side and a suction side. FIGURE 4.2.6-3 Computational domain for a flat plate In order to be compatible with the transition model, a 3D mesh should be used for this case with a correct orientation: i perpendicular to the flat plate with i=1 on the flat plate and with j and k along the plate: k in streamwise direction and j perpendicular to main flow direction. The .bcs file of the mesh should be modified in order to include the turbomachinery blade definition. At the end of the .bcs file the line "NUMBER_OF_BLADES 0" should be modified: the "0" should be change in a "1" as the flat plate will be considered as one blade (of zero thickness). 4-20 FINE™/Turbo Mathematical Model Flow Model Next lines need to be added as shown here: 4-2.7 Gravity Forces When gravity should be taken into account the box Gravity Forces should be checked. If gravity is activated, three input dialog boxes appear to define the Gravity Vector. The default gravity vector is defined as: (gx, gy, gz)=(0,-9.81,0) [m/s2], representing the gravity on Earth where the y-axis is oriented normal to the ground. When the gravity is taken into account in the Navier-Stokes equations, the source terms ρg and ρ ( g ⋅ v ) are respectively introduced in the momentum and energy conservation equations where ρ is the density, g the gravity vector and v the velocity vector. If the fluid is a liquid, the density is constant and there is no influence of the pressure or temperature on the flow by interaction with the gravity. To simulate these interactions, one can use the Boussinesq approximation in the gravity source terms. With this approximation, the density is developed in the first order of the MacLaurin series. It becomes: ρ = ρ ref ( 1 + α ( p – p ref ) – β ( T – T ref ) ) (4-19) with α the compressibility and β the dilatation coefficients specified in the fluid properties. FINE™/Turbo 4-21 Flow Model Characteristic & Reference Values This variation of the density is only applied to the gravity source term (Boussinesq approximation). Otherwise, the density is kept constant in the conservation equations. The value of ρ ref is the characteristic density specified in the Configuration/Flow Model page. p ref and T ref are the reference values in the Configuration/Flow Model page. When the gravity is taken into account, a reference pressure must be specified at a reference altitude to add the hydrostatic pressure in the initial pressure field. The reference pressure is the reference value in the Configuration/Flow Model page. The reference altitude is specified in the expert parameter IREFPT in meter [m]. 4-2.8 Low Speed Flow (Preconditioning) This option appears in the Flow Model page only if the fluid type is compressible. Preconditioning is automatically used for incompressible fluids. In the low Mach number regime, time-marching algorithms designed for compressible flows show a pronounced lack of efficiency. When the magnitude of the flow velocity becomes small in comparison with the acoustic speeds, time marching compressible codes converge very slowly. Two low speed preconditioners, Hakimi and Merkle preconditioners, have been implemented in the FINE™/Turbo solver in order to provide fast convergence characteristics and accurate solutions as the Mach number approaches zero: • The Hakimi preconditioner is of sufficient generality and can treat any type of fluids and flows. Efficient convergence rates and accurate solution can be obtained for Mach numbers from M=0.1 to M=10-6, Reynolds numbers from Re=106 to 10-6 and aspect ratios from 1 to 2000. • Compared with the Hakimi preconditioner, the Merkle preconditioner has the advantage that it is not only effcient at all Mach number but also at all Reynolds and Strouhal numbers. With the Merkle preconditioner, the user can perform a fast and accurate computation of supersonic flows with regions at very low speed. Moreover the Merkle preconditioner doesn't require any user inputs. Merkle preconditioning is not compatible with: •barotropic fluids •unsteady mode •cavitation model For the detailed parameter settings, please refer to section 6-2.2.4. 4-3 Characteristic & Reference Values 4-3.1 Reynolds Number Related Information The user has to specify some characteristic values (length, velocity and density). These values are used to calculate the Reynolds Number (only plotted when the kinematic viscosity is constant) that provides a useful information to choose the suitable model (section 4-2.5). These characteristic values can be used for other purposes as well. 4-22 FINE™/Turbo Characteristic & Reference Values Flow Model The characteristic length is used: — in the outlet boundary condition for which the mass flow is imposed with pressure adaptation, — in the computation of CP1 and CP3 for cylindrical cases. — in the transition model, to set the free stream turbulent intensity. The characteristic velocity is used: — in the preconditioning method to compute the parameter β, — in the computation of the solid data Cf (normalized by ( ρ ref U 2ref ⁄ 2 ) ). The characteristic velocity should be set to the highest value in the flow domain. The characteristic density is used: — in the Boussinesq approximation for incompressible fluid (Eq. 4-19), — in the computation of the solid data Cf (normalized by ( ρ ref U 2ref ⁄ 2 ) ), — in the evaluation of the Reynolds number only when the dynamic viscosity of the fluid is specified in the Sutherland law on the Fluid Model page. 4-3.2 Reference Values The reference values have been introduced for preconditioning, to define a gauge pressure and a gauge total energy. A value of Reference temperature Tref of the order of magnitude of the expected temperature field will reduce the machine round-off errors influence on the temperature field. The value of Reference pressure Pref fixes the absolute level of the pressure in the field. This value is used in the equation of state for a compressible fluid and in the second order artificial dissipation term. A value of Pref close to the real pressure level is therefore recommended. These reference values also have some additional uses which are described hereafter: — in the Boussinesq approximation for incompressible fluid (Eq. 4-19), — in the outlet boundary condition for which the mass flow is imposed with pressure adaptation, FINE™/Turbo 4-23 Flow Model Characteristic & Reference Values — in the definition of the heat transfer coefficient when the expert parameter HTCDEF is set to 2, see section 10-2.1.5. 4-24 FINE™/Turbo CHAPTER 5: 5-1 Boundary Conditions Overview During the IGG™ grid generation process, the user has to define the type of boundary condition to be imposed along all boundaries. The parameters associated with these boundary condition types can be fully defined using the Boundary Conditions page. This chapter gives a description of the boundary conditions, available in the Boundary Conditions page. In section 5-2, the page is described. For expert use, section 5-3 gives an overview of the available expert parameters. In section 5-4, some advice is provided on the combinations of boundary conditions to use. 5-2 Boundary Conditions in the FINE™/Turbo GUI When selecting the Boundary Conditions page the "parameters area" appears as shown in Figure 5.2.0-1. Five tabs are available, depending on the boundary condition types defined in the mesh. There are currently five types of boundary conditions available in the FINE™/Turbo solver: inlet, outlet, periodic (connection with or without rotational or translational periodicity), solid walls and external (far-field). Each of those is described in the next sections. Note that the connecting (matching (CON) and non-matching (NMB)) boundary conditions (without periodicity) do not appear in this menu, because they do not require any input from the user. Only the "periodic" conditions (PER & PERNM) appear in the Periodic tab page. Note that the full non matching and periodic full non matching connections defined within IGG™ (refer to IGG™ User Manual for details on limitations) are appearing in the Solid tab page. A common particularity of the five boundary conditions pages is their subdivision into two areas. The left area contains always a list of the different patches that are of the boundary condition type of the selected tab page. A patch can be identified either by the name of the block face to which it FINE™/Turbo 5-1 Boundary Conditions Boundary Conditions in the FINE™/Turbo GUI belongs and by its number, or by the numbers of the block and face and by its local index on the face (if no name is provided in IGG™). The right area is the area where the boundary condition parameters are specified for the selected patch(es). FIGURE 5.2.0-1 Boundary Conditions page One or several patches may be selected in the left area by simply clicking on them. Clicking on a patch unselects the currently selected patch(es). It is possible to select several patches situated one after another in the list by clicking on the first one and holding the left mouse button while selecting the next. To select a group of patches that are not situated one after another in the list, the user should click on each of them while simultaneously holding the key pressed. Several patches can be grouped by selecting them and clicking on the Group button. A dialog box will appear asking for a group name. The name of the group will appear in red color in the list of patches to indicate that this is a group of patches. Every change in the parameters when a group is selected applies to all patches in the group. The Ungroup button removes the group and its patches are displayed individually in the list. The Ungroup button is active only when at least one group is selected. Clicking with the left mouse button on the plus sign + left of a group name in the list will display the patches included in this group. If some of the patches have been given names in IGG™, these names will appear in FINE™/Turbo. If the patches have been grouped in IGG™, by giving the same name to many patches, they will appear ungrouped in FINE™/Turbo (with block, face and patch number shown after the name) to avoid contradiction between grouping in IGG™ and FINE™/Turbo. Ungroup button will toggle the IGG™ name of the selected patch(es) with the default FINE™/Turbo name (block, face and patch number). If the Use Grid Configuration option is activated when linking the mesh for the first time (see section 2-2.3), a default grouping by row is proposed by FINE™/Turbo. For 5-2 FINE™/Turbo Boundary Conditions in the FINE™/Turbo GUI Boundary Conditions the solid boundaries, the rotation speed specified in IGG™ or AutoGrid™ is automatically transferred to FINE™/Turbo. This limits the user input to a strict minimum. This automatic grouping cannot be modified by the user. If the graphics area with the mesh topology of the project is opened (Mesh/View On/Off menu), all the selected patches and/or groups will be highlighted. A click with the right mouse button over a selected patch will select all the patches and groups in the list that have the same parameters. If the user selects several patches that have different parameters, a warning dialog box will appear. When clicking on OK all parameters will be set equal to the ones of the first patch. Selecting Cancel instead will cancel the selection. (1) (2) (3) FIGURE 5.2.0-2 Two patches will be grouped into a group called HUB. The right area of all the notebook boundary condition pages is created in a generic way by means of a resource file, where all the boundary condition parameters are described altogether with their default values. Some boundary conditions are only available for an incompressible, compressible or condensable gases. FINE™/Turbo will automatically disable the boundary conditions that are not available, depending on the type of fluid selected in the Fluid Model page. Also the type of boundary conditions are adjusted according to the selection for Cartesian or cylindrical boundary conditions. The five pages associated to each of the five types of boundary conditions are described in detail in the following sections. FINE™/Turbo 5-3 Boundary Conditions 5-2.1 Boundary Conditions in the FINE™/Turbo GUI Inlet Condition 5-2.1.1 Available Types The inlet boundary condition page is customized according to the configuration of the project (Cartesian or cylindrical) as shown in the following two figures. The user has the freedom to access both types of configuration in the Boundary Conditions page independently of the mesh properties. 5-4 FIGURE 5.2.1-3 Subsonic inlet boundary conditions page for cylindrical problems. FIGURE 5.2.1-4 Subsonic inlet boundary conditions page for Cartesian problems. FINE™/Turbo Boundary Conditions in the FINE™/Turbo GUI Boundary Conditions The upper part of the inlet boundary condition page allows the user to select the type of inlet condition to apply to the selected patches through a series of toggle buttons. There are two categories of inlet conditions: conditions applicable to Subsonic inlets and conditions applicable to Supersonic inlets. Note that to determine whether an inlet (or an outlet) boundary is subsonic or supersonic, the velocity component normal to the boundary should be considered. Total quantities imposed condition applicable to supersonic inlets is not compatible with condensable fluid. For each inlet condition type, the lower part of the page is adapted in order to provide input boxes only for the physical variables that are required to fully determine the boundary condition. These variables are for instance: the pressure and temperature (static or total), the velocity components, the velocity magnitude, the velocity angles (specified in radians), or the mass flow. In case of a simulation using a k-ε, k-ω or v2-f turbulence model, the inlet values of the parameters k and ε are also required. A turbulent viscosity entry appears in case the Spalart-Allmaras turbulence model is used. For the inlet boundary conditions: • The velocity components are defined in the Cartesian or cylindrical coordinate system, depending on the selected type • The pressure and the temperature values to specify can be the static or the total values • For rotating configurations, the specified values are the absolute quantities • A special condition is available, for which the values can be entered in the upstream rotational frame of reference Six major types of inlet boundary conditions can be identified: • velocity components and the static temperature • total pressure, total temperature and the flow direction Total quantities imposed boundary conditions with V-extrapolated is incompatible with a model which streamwise direction is in negative Z. • total enthalpy, dryness fraction and the flow angles (only for condensable fluid) It should be mentioned that the use of this boundary condition requires the presence of the saturation table ("PSA.atab") of the fluid in the corresponding subfolder. The boundary condition is based on the dryness fraction (X), whose value is bounded between 0 and 1. The inlet thermodynamic must be either saturated or be located inside the biphasic zone. The validity of the condensable fluid model is limited to gases with small fraction of liquid (X > 0.9) or reversely to liquids with small fraction of gas (X < 0.1). • mass flow, static temperature and the flow direction (see the next paragraph for detail on coupling with the outlet) The mass flow imposed in the GUI will be used for the whole inlet. For example, if the user has a rotational periodicity of 40, the mass flow for only one passage will be the mass flow specified in the GUI divided by 40. • distributions of the flow variables for the non-linear harmonic method. For more detail, please refer to Chapter 8-4.2.2. FINE™/Turbo 5-5 Boundary Conditions Boundary Conditions in the FINE™/Turbo GUI • conditions set from a rotor-stator interface (SubProjects only, see Chapter 8-11) Inlet boundary condition Velocity normal to inlet is not compatible with the following expert parameter value: •INITRB=0 •IMASFL=1 •INMFTT=1 Moving grid is not compatible with relative velocity normal to inlet when using mass flow imposed. 5-2.1.2 Coupling Temperature with Outlet When the mass flow is imposed at an inlet patch, the temperature may be chosen to be coupled to an outlet patch. The coupling is performed through the static temperature. Only in that case, the average temperature Taverage is computed at the specified outlet and imposed at the inlet as Tinlet = Taverage + ΔT (see Figure 5.2.1-5). The quantity ΔT is a constant temperature difference (>=0 or <0) specified by the user. This is done in FINE™/Turbo by choosing Mass Flow Imposed as boundary condition type for the subsonic inlet in cylindrical configuration and clicking on the Coupling Temperature With Outlet button. A pull-down menu allows to select which patch of the outlet must be involved in the coupling. The value to be entered in the static temperature box is ΔT. This option is only working if both inlet and coupled outlet patch have the mass flow imposed as a boundary condition. Taverage Outlet Taverage + ΔT Inlet FIGURE 5.2.1-5 Meridional view of the "Coupling with Outlet ID" functionality 5-2.1.3 Imposing Variables as an Interpolation Profile Each variable can be defined as constant or as an interpolation profile of the variable. The imposed boundary condition may be variable in space (one or two dimensions) and/or in time (in case of an unsteady calculation). To visualize and/or edit the profile data press the small button ( ) on the right side of the label "profile data". This button opens the Profile Manager with the existing profile. See section 2-7 for a 5-6 FINE™/Turbo Boundary Conditions in the FINE™/Turbo GUI Boundary Conditions detailed description of the Profile Manager. It offers the possibility to modify or to create a data profile interactively. Click on the OK button to set the new profile to the selected patch(es). FIGURE 5.2.1-6 The Profile Manager The option Surface data toggles 1D and 2D editing modes. It can be used to change the dimension of an existing profile. 2D profiles are displayed as a "cloud of points". Selecting a point will display the f(x,y) value in blue in the corresponding column of the Profile Manager. More details on the required file format are available in Appendix A. If a quantity is defined as a function without the definition of a valid profile a warning message will appear when saving the project or opening a new page or tab page. In such a case a default constant value is used in the computation. 5-2.2 Outlet Condition For a supersonic outlet all variables are extrapolated. An outlet is considered as supersonic on the basis of the normal velocity direction to the boundary. Five types of subsonic outlet boundary condition are available, as shown in Figure 5.2.2-7. These five different boundary conditions are described in the following paragraphs. An option for treatment of Backflow Control can be activated in the case of radial diffusers outlet. The purpose of this option is to control the total temperature distribution along the exit section. In case the flow partially re-enters the domain through the boundary, the total temperature of the entering flow is controlled so that the entering and outgoing flows globally have the same total temperature. Backflow Control is only compatible with compressible fluid. When condensable or incompressible fluids are used, it is suggested to use the expert parameter BCKFLO to control backflow at outlet, see Chapter 5-3.5 for more detail. Backflow Control is applied separately on each outlet patch when an uniform static pressure is imposed (it is applied to a group of patches if averaged static pressure and mass flow are imposed). FINE™/Turbo 5-7 Boundary Conditions Boundary Conditions in the FINE™/Turbo GUI Backflow Control is not available for the outlet boundary conditions where static pressure is imposed with radial equilibrium. FIGURE 5.2.2-7 Outlet boundary conditions page. 5-2.2.1 Pressure Imposed There are three different methods to impose the pressure at the outlet: • Static Pressure Imposed: the static pressure is imposed on the boundary, the static temperature and the absolute velocity components are extrapolated. As described for the inlet conditions, the static pressure can be constant or defined as a data profile. • Averaged Static Pressure: if imposing an uniform static pressure at the outlet is not an appropriate approximation of the physical pressure distribution at the outlet, an averaged static pressure may be used. In this case only an averaged value for the static pressure is imposed while the pressure profile (around this average) is extrapolated from the interior field. The outlet patches have to be grouped in one group to use this boundary condition. • Radial Equilibrium: This boundary condition is applicable only to cylindrical problems. It is adapted for a patch in which the mesh lines in the circumferential direction have a constant radius. The outlet static pressure is then imposed on the given radius and the integration of the radial equilibrium law along the spanwise direction permits to calculate the hub-to-shroud profile of the static pressure. Please note that the given radius should be between hub and shroud. Otherwise the outlet static pressure will be imposed on the corresponding extreme radius of the outlet instead of the given radius. A constant static pressure is imposed along the circumferential direction. This boundary condition is only valid on surfaces with mesh lines at constant radius. This boundary condition is not compatible with the radius r=0. 5-8 FINE™/Turbo Boundary Conditions in the FINE™/Turbo GUI Boundary Conditions The pressure imposed at the outlet, can be constant or as a function of space and/or time. To define a profile as a function of space and/or time click on the profile button ( ) right next to the input text box. The Profile Manager will appear as described in section 5-2.1.3. 5-2.2.2 Mass Flow Imposed When imposing the mass flow at the outlet, the related patches must be grouped. This permits to have several groups of patches, each of the groups constituting an outlet through which the mass flow can be controlled. Two different techniques are available to impose the mass flow: • Velocity Scaling: the pressure is extrapolated and the velocity vector is scaled to respect the mass flow. This technique is only valid for subsonic flows, and is not recommended in case of significant back flows along the exit boundary. • Pressure Adaptation: this boundary condition is identical to the ’Static Pressure Imposed’ or ’Radial Equilibrium’ boundary conditions, except from the fact that the exit pressure is automatically modified during the resolution process so that after convergence, the prescribed mass flow is obtained. The pressure asked in addition to the imposed mass flow with both options is only used to create the initial solution and for the full-multigrid process, during which a uniform static pressure outlet condition is used. When using the mass flow imposed outlet boundary condition and restarting a computation from a file, only one group of patches can be used in the initial solution page and the reset convergence history has to be deactivated The outlet patches have to be grouped in one group to use this boundary condition. The mass flow imposed in the GUI will be used for the whole outlet. For example, if the user has a rotational periodicity of 40, the mass flow for only one passage will be the mass flow specified in the GUI divided by 40. 5-2.2.3 Averaged Mach Number When imposing the averaged Mach number at the outlet, the user must group all the related patches for each outlet. This permits to have several groups of patches, each of the groups constituting an outlet through which the averaged Mach number can be controlled. Two options are available: • Absolute Mach Number with Pressure adaptation: the absolute Mach number is imposed at the outlet boundary. The exit pressure is automatically modified during the resolution process so that after convergence, the prescribed absolute Mach number is obtained. • Relative Mach Number with Pressure adaptation: the relative Mach number is imposed at the outlet boundary. The exit pressure is automatically modified during the resolution process so that after convergence, the prescribed relative Mach number is obtained. The initial pressure asked in addition to the imposed Mach number is used in the full multigrid initialisation. This value is also used for the turbomachinery initial solution. During the pressure adaptation process, the exit pressure can be imposed in different ways: • Constant Profile: this boundary condition is identical to the ’Static Pressure Imposed’ boundary condition. FINE™/Turbo 5-9 Boundary Conditions Boundary Conditions in the FINE™/Turbo GUI • Radial Equilibrium: this boundary condition is identical to the ’Radial Equilibrium’ boundary condition. • Extrapolated Profile: this boundary condition is identical to the ’Averaged Static Pressure’ boundary condition. The averaged Mach number boundary condition at outlet is not compatible with incompressible fluid. 5-2.2.4 Characteristic Imposed This boundary condition has been implemented to increase the robustness in the frame of a design process and is only available when using a perfect or real gas in the Fluid Model page. Figure 5.2.2-8 shows as an illustration performance curves for a centrifugal compressor. Near choking conditions the mass flow stays almost constant with a variation of the pressure. Therefore, it is recommended in this region, to impose the static pressure at the outlet. Near stall however, the pressure varies only slightly with varying mass flow. Therefore, it is recommended in this region of the performance curve, to impose the mass flow at the outlet instead of the static pressure. (static pressure) (mass flow) FIGURE 5.2.2-8 Example of performance curves for centrifugal compressor In a design process, with a variation of the geometry, it is not always known in advance where in the performance curve the computations are performed. Therefore it is not always possible to choose the appropriate boundary condition at the outlet for the complete design process. To overcome this problem this boundary condition allows to impose a relation between the mass flow and the pressure at the outlet. It is no longer needed to choose between imposing pressure when working around the chocking part and imposing mass flow when working close to the stall limit. The user has to impose a very simple characteristic line defined through 3 parameters: a target outlet mass flow and a target outlet pressure (at point 2 in Figure 5.2.2-8) and the pressure at zero mass flow (point 1 in Figure 5.2.2-8). Based on these three parameters, a simple parabolic curve is generated. This curve is then used to apply the boundary condition allowing to impose a relation between the mass flow and the pressure at the outlet. 5-10 FINE™/Turbo Boundary Conditions in the FINE™/Turbo GUI Boundary Conditions 5-2.2.5 From Rotor/Stator The outlet boundary condition From Rotor/Stator can only be used in the frame of the SubProject module. This boundary condition is set automatically, no user intervention is required. For more details, see Chapter 8-11. 5-2.3 Periodic Condition One important feature of the IGG™ mesh generator concerns the automatic establishment of all connecting and periodic boundary conditions. The corresponding information is transmitted to the FINE™/Turbo interface, with the advantage that the user does not need to specify any input concerning these boundary conditions. Normally no user input is required on this page. The only periodic boundary condition cases for which a user input is required are those in which some of the boundary conditions have to be applied with a periodicity angle that differs from the global periodicity angle of the block. FIGURE 5.2.3-9 Periodic boundary condition page. In case some input is required this section explains how to define the periodic conditions using the PERIODIC tab page. The type of periodicity connection between the patches (Matching or Non Matching) can be entered. A connection is Matching if the numbers of mesh points along the connected patches are identical, and if all the corresponding points along these patches coincide (PER type within IGG™). The Non Matching connection (PERNM type within IGG™) requires the use of an interpolation process to establish the connection, whereas a matching one consists of a single communication of the flow variables. The interpolation used for non matching periodic boundaries consists on a linear interpolation from the four nearest cells. Some additional characteristics need to be given to fully determine the periodic boundary condition: FINE™/Turbo 5-11 Boundary Conditions Boundary Conditions in the FINE™/Turbo GUI • For Cartesian (rectangular) problems, the user has to specify the translation vector defining the periodicity. The positive translation vector goes from the current patch to the periodicity patches. • For cylindrical problems, the user has to specify the rotation angle in degrees. The rotation angle is calculated from the connected patch to the current patch, according to the rule of the right handed system. 5-2.4 Solid Wall Boundary Condition The solid wall boundary condition page is customized essentially according to the type of calculation (inviscid or viscous). For Euler cases (i.e. inviscid), no parameter is requested for the wall boundary conditions. For Navier-Stokes cases, the box at the top of the page allows to set both velocity and thermal conditions. The type of boundary conditions determines the way the velocity and thermal conditions are defined for the solid boundary. 5-2.4.1 Cylindrical Boundary Condition a) Area Defined Rotation Speed The wall rotation velocity can be constant or area defined (see Figure 5.2.4-10). The area defined option allows to attribute a specific rotation velocity to a rectangular zone in the meridional plane independently of the grid structure. When the area defined option is selected, a small picture defining the parameters is displayed (the z axis is the rotation axis, the r axis is the radial axis). The rotation velocity is set to ω 1 outside the domain and to ω 2 inside the domain. The specified range must be a valid range for the used geometry. For example, for an axial machine the limits for rotation of the hub can be defined by setting the lower and higher axial limit to appropriate values. In such a case it is important to set the radial limits such that they include the full solid (hub) patch. 5-12 FINE™/Turbo Boundary Conditions in the FINE™/Turbo GUI FIGURE 5.2.4-10 Solid Boundary Conditions boundary conditions page in case of a cylindrical boundary condition b) Thermal Condition Four options are available for the thermal condition: • Adiabatic • Imposed Heat Flux (in W/m2) A positive heat flux indicates that the direction of the heat flux is from the solid wall to the fluid. • Imposed Temperature (isothermal) • Imposed heat transfer coefficient (W/K/m2) qw h = --------------------------------- , ( T ref – T wall ) where q w is the local heat flux, T wall the local temperature at the wall and T ref the reference temperature inputted by the user. The imposed heat flux, temperature or heat transfer coefficient can be constant on the patch or defined as a profile. Use the pull down menu to change Constant Value to for example fct(space). Click on the profile button to launch the Profile Manager as described insection 5-2.1.3. 5-2.4.2 Cartesian Boundary Conditions The user can define a translation or a rotation velocity vector. In the latter case, the coordinates of the rotation centre are requested. The thermal conditions are similar to those for cylindrical flows. FINE™/Turbo 5-13 Boundary Conditions Boundary Conditions in the FINE™/Turbo GUI 5-2.4.3 Force and Torque Below the box, a Compute force and torque option is provided that permits to include the selected patches in the calculation of the global solid boundary characteristics. The contribution of patches included in a full non-matching connection will not be taken into account for the computation of the force and torque. Those patches will however appear as solid in the boundary condition page. For a cylindrical project (as defined in Mesh/Properties) in an internal flow (the expert parameter IINT set to 1 as by default): — the axial thrust, i.e. the projection of the global force on the rotation axis, — the torque, i.e. the couple exerted by the global force, calculated at (0,0,0). These quantities are often calculated on the rotating walls. They are calculated from the pressure and the velocity fields on the walls. The axial thrust is computed as: F ⋅ nz . (5-1) S The computed force is the one from fluid on solid. The force is considered as positive when in the direction of the z-axis. The projection of the torque along a given direction z , i.e. the couple exerted by the global force along the rotation axis: r × F ⋅ z S (5-2) In all other cases the force and torque are computed as: — the lift, — the drag, — the moment calculated at (0,0,0) by default. The direction of the forces and torque as well as the location of the point for the moment can be determined with the expert parameters IDCLP, IDCDP, IDCMP and IXMP (see section 5-3). When using an area defined rotation speed, the expert parameter TORRO can be used to compute the force and torque on the complete patch, or on the rotating part only (see section 5-3). Within the FINE™/Turbo solver it is possible to calculate and to store the partial torque in the corresponding ".wall" file of the computation through the use of the expert parameter IFRCTO within the FINE™/Turbo GUI. The partial torque is the torque computed for each layer on the whole blade. When IFRCTO is set to 2 (1 or 3), the torque is defined on each J-direction (I-direction or K-direction) layer (i.e. when using AutoGrid™ meshes, J-direction corresponds to the spanwise direction). 5-14 FINE™/Turbo Boundary Conditions in the FINE™/Turbo GUI Boundary Conditions IFRCTO = 2 Total Torque and Force on Suction Side Partial Torque and Force on Suction Side • 56 = 56 sublayers in J-direction (spanwise) • column 1: %span corresponding to the layer • column 2: Fx on the sublayer • column 3: Fy on the sublayer • column 4: Fz on the sublayer IFRCTO = 0 Total Torque and Force on Suction Side FIGURE 5.2.4-11 File ".wall" when computing partial torque along the blade Finally, the resulting ".wall" will contain, in addition of the global torque and force on the selected blade, the partial torque for each layer along the J-direction of the blade as presented in Figure 5.2.4-11. The force and torque computed on the selected surface(s) and included in ".wall" file are based on the full 360 degrees, so taking into account the periodicity when the blocks concerned are presenting a periodicity. 5-2.4.4 Properties of Solid for Turbulence In addition, when turbulence models with extended wall function are used, the user has to specify the type of wall ("Smooth" or "Rough") and the following constants: the Von Karman constant κ and the B constant. If the wall type is rough, the equivalent roughness height k0 and the height of the zero displacement plane d0 are also required. A description of these constants is provided in the theoretical manual. Two methods considering the wall function for roughness is implemented. With the old method (default, IROUGH=0), the constant B has to be computed after obtaining the value of y+. And the value of B will also correct y+. The user has to iterate this procedure and converge to the desired FINE™/Turbo 5-15 Boundary Conditions Boundary Conditions in the FINE™/Turbo GUI value of B. This is not straighforward and a new approach has been introduced in the flow solver in order to simplify the computations with roughness. To use the new method, the user has to set the expert parameter IROUGH to 1. When a rough wall is specified, if IROUGH=0, the distance from the wall to the cellcentre of the first inner cell should be bigger than k0 + d0; if IROUGH=1, the distance from the wall to the cell-centre of the first inner cell should be bigger than ks + d0. In general, the first inner cell should be located within the fully turbulent layer. The application field of the ’law of the wall’ imposes restrictions on the grid. The user is strongly advised to check the conformity of this grid with these conditions (see section 4-2). 5-2.5 External Condition (Far-field) The external boundary condition is provided to treat the far-field boundaries when dealing with external flow computations (the expert parameter IINT=0). An example is given in Figure 5.2.5-12. This type of boundary condition determines whether the flow is locally entering or leaving the flow domain and uses the theory of the Riemann invariants to act consequently on the appropriate variables. Depending on the chosen turbulence model, five or seven input boxes are provided to specify the free-stream values of the variables to be used in the boundary condition formulation. FIGURE 5.2.5-12 External (far-field) boundary conditions page. Use an external condition rather than an inlet condition for cases for which it is not known if the flow enters or leaves the domain. Condensable gases are not compatible with external boundary condition. The boundary condition External Constant Wind with Incidence Relative to Axis Z is only compatible with NLH. 5-16 FINE™/Turbo Expert Parameters Boundary Conditions 5-3 Expert Parameters 5-3.1 Imposing Velocity Angles of Relative Flow In case of a stator calculation it may be convenient to impose the velocity angles of the relative flow at the exit of the upstream rotor. In case of rotors, the user may also prefer to impose relative boundary conditions. This procedure is only available when total conditions and flow angles are imposed. In addition to that the extrapolation of Vz must be selected. Note also that both flow angles and total conditions are then treated in the relative mode. The following parameters have to be defined: INLREL(integer): allows to specify relative angles for the cylindrical inlet boundary conditions with = 0 (default):total quantities imposed, = 1: inlet for a stator (extrapolation of the axial velocity only). The expert parameter OMGINL has also to be specified, = 2: inlet for a rotor. ANGREL(real): data use with the expert parameter INLREL (for stator only). This variable contains three values: • 1st real: relaxation angle (in degrees), • 2nd real: distance (%) from hub where the absolute flow angle is extrapolated, • 3rd real: distance (%) from shroud where the absolute flow angle is extrapolated. 5-3.2 Inlet Mass Flow Boundary Condition IMASFL(integer): expert parameter specially dedicated to radial inlets. The mass flow is extrapolated instead of the velocity for the cylindrical inlet boundary conditions with imposed total quantities: = 0 (default): treatment inactive, the velocity is extrapolated, =1: option activated, extrapolation of the mass-flow. INMFTT(integer): specify static temperature or total temperature when using mass flow imposed inlet BC, = 0 (default): static temperature is specified. =1: total temperature is specified. 5-3.3 Outlet Mass Flow Boundary Condition RELAXP(real): is the under-relaxation for the outlet boundary condition where the mass flow is imposed with the exit pressure adaptation (default value = 1.). VELSCA(real): is the maximum value allowed for the velocity scaling (outlet boundary condition with mass flow imposed by scaling velocity) (default value = 2.) FINE™/Turbo 5-17 Boundary Conditions 5-3.4 Outlet Averaged Mach Number Boundary Condition RELAXP(real): 5-3.5 Expert Parameters is the under-relaxation for the outlet boundary condition where the averaged Mach number is imposed with the exit pressure adaptation (default value = 1.). Control of backflows BCKFLO(integer): defines whether an Euler wall boundary condition is used at all outlet cells where back flow is detected: = 0 (default): don’t use the control of backflow, = 1: use an Euler wall boundary condition at all cells where backflow is detected. BCKFLU(integer): defines whether the backflow control at inlet is activated or not. The use of BCKFLU is limited to turbomachinery cases meshed with AutoGrid4™/ AutoGrid5™. = 0 (default): don’t use the control of backflow at inlet = 1: use the control of backflow at inlet, based on pitchwise averaging of the solution. 5-3.6 Torque and Force IDCDP(real): if cylindrical project (as defined in Mesh/Properties) and IINT=1: direction (x,y,z) of axial thrust, in all other cases: direction (x,y,z) of drag. IDCLP(real): direction (x,y,z) for lift (not used if cylindrical project and IINT=1), IDCMP(real): direction (x,y,z) for moment, IFRCTO(integer): calculate and to store the partial torque in the corresponding ".wall" file. More detail in Chapter 5-2.4.3. IXMP(real): coordinate (x,y,z) of the point around which the moment has to be calculated. The coordinates are expressed in meters. TORRO(integer): = 0 (default): Compute force and torque on the complete patch = 1: Compute force and torque only on the part of the patch which is defined through an area defined rotation (the part corresponding to ω2). IMUWAL(integer):if set to 1, the ".wall" file will be saved at each iteration on the finest grid level (current grid level specified in the Numerical Model page) when performing a steady simulation. The corresponding .wall file (_iter#.wall) will be saved in the computation directory. 5-3.7 Euler or Navier-Stokes Wall for Viscous Flow If the flow type selected is laminar or turbulent Navier-Stokes, it is possible in Expert Mode to choose between an Euler wall (zero normal velocity) and a Navier-Stokes wall (no-slip condition). Further details on the numerical treatment of the walls are provided in the theoretical manual. Note that the default (active in Standard Mode) is a Navier-Stokes wall. 5-18 FINE™/Turbo Best Practice for Imposing Boundary Conditions 5-3.8 Boundary Conditions Pressure Condition at Solid Wall When the interface is in Expert Mode, two toggle buttons are provided to select the type of pressure condition at the wall: extrapolated or computed from the normal momentum equation. The default (active in Standard Mode) is the extrapolation of the pressure. 5-4 Best Practice for Imposing Boundary Conditions The quality of the flow simulation depends primarily on the quality of the grid and the imposed boundary conditions. In this section the most adapted boundary conditions are proposed according to the type of studied flow. In case a calculation is diverging, it is strongly recommended to check by post processing of the solution (in CFView™), that the appropriate boundary conditions have been imposed. 5-4.1 Compressible Flows For compressible flows it is recommended that the inlet boundary condition fixes the absolute total quantities (pressure, temperature) and the flow angles and that the outlet boundary condition fixes the static pressure (exit pressure). This exit pressure can be imposed as: • a constant value along the exit, • an average value at the exit, • the pressure at mid-span for radial equilibrium (only for an axial outlet). The static pressure at the exit of the domain is rarely constant. It is thus advised to impose the pressure as an average value or as a initialization data for radial equilibrium. Even if this value of pressure is known, for numerical reasons it is possible that the computed massflow differs from the expected one. It is thus necessary to modify the exit pressure repeatedly until obtaining the accurate mass-flow. This procedure can be numerically expensive especially if the calculations are carried out on a fine grid. A solution to overcome this drawback is to impose the mass-flow at the outlet. This can be done in two ways: • Velocity Scaling: for a low subsonic outlet (Mach number lower than 0.4) this condition fixes the mass-flow at a given control surface by scaling the vectors on this surface. This is not as robust as to impose the exit pressure and is not recommended in case significant backflows are detected along the exit. If this is the case, the next option is better suited. • Pressure Adaptation: in this case, an automatic procedure introduces a variation of the imposed exit pressure at each iteration of the calculation. The pressure is then iteratively updated in order to reach at convergence the imposed mass-flow. This is not as robust as to impose the exit pressure, but is more robust than the velocity scaling option. FINE™/Turbo 5-19 Boundary Conditions 5-4.2 Best Practice for Imposing Boundary Conditions Incompressible or Low Speed Flow For incompressible or low speed flows it is recommended to impose the mass-flow and the static temperature at the inlet and a static pressure at the exit. This couple of inlet-outlet conditions has a stabilizing effect on calculations and is also well adapted to provide initial solutions for multi-stage calculations. 5-4.3 Special Parameters (for Turbomachinery) In case of flow separation at the outlet of radial diffusers it is recommended to use the backflow treatment option. This option can be activated by activating Backflow Control in the FINE™/ Turbo GUI on the Boundary Conditions page under the OUTLET tab page. Radial turbine FIGURE 5.4.3-13 Example of case with strongly varying radius in the inlet1 When end-walls in the inlet regions are strongly varying in radius (e.g. centripetal turbines as in Figure 5.4.3-13) or in case of highly tangential inlet flow angles it is advised to use the IMASFL expert parameter (in the list of expert parameters on the Control Variables page in Expert Mode). This option is adapted when the inlet boundary conditions fixes the absolute total quantities (pressure, temperature) and is only valid for non-preconditioned computations. When it is activated, the mass-flow is extrapolated instead of the velocity. Inlet patches have to be grouped in one group to use the extrapolation of mass flow boundary condition. 1. Picture from D. Japikse, N.C. Balines, Introduction to Turbomachinery, Concept ETI Inc. and Oxford University Press, 1994. 5-20 FINE™/Turbo CHAPTER 6: 6-1 Numerical Scheme Overview This chapter describes the interface and settings that can be used to specify the numerical parameters and the time configuration for the simulations: • Numerical Model defines the numerical aspects of the computations • Time Configuration defines the time dependence of the equations to solve. This chapter is organised as follows: • section 6-2 describes the interface and settings for the definition of the numerical model, • section 6-3 describes the interface and best practice for unsteady computations. 6-2 Numerical Model 6-2.1 Introduction To define numerical parameters of the computation, the Numerical Model page allows to define several aspects of the computation: • the CFL number, • the multigrid parameters, • preconditioning parameters (if applicable). These parameters are described in the next section. FINE™/Turbo 6-1 Numerical Scheme Numerical Model FIGURE 6.2.1-1 Numerical model interface In expert user mode (Expert Mode) additional parameters are available as shown in Figure 6.2.1-2: additional multigrid parameters and unsteady parameters. These interfaced expert parameters are described in section 6-2.3. Also the non-interfaced expert parameters are described in this section. More theoretical information on the available parameters related to the numerical model (spatial and temporal discretizations) is provided in Chapter 5-2 in the theoretical manual. FIGURE 6.2.1-2 Numerical 6-2.2 Model page in expert mode Numerical Model in the FINE™/Turbo GUI 6-2.2.1 CFL Number This box allows to tune the CFL (Courant-Friedrich-Levy) number to be employed in the computation. This number globally scales the time-step sizes used for the time-marching scheme of the flow solver. A higher value of the CFL number results in a faster convergence, but will lead to divergence if the stability limit is exceeded. 6-2 FINE™/Turbo Numerical Model Numerical Scheme 6-2.2.2 CPU Booster FINE™/Turbo includes an innovative breakthrough in convergence acceleration. Based on enhanced implicitness, it leads to a drastic reduction in computational time with respect to the current advanced technologies in FINE™/Turbo. If the user activates the option CPU Booster, the default value of the CFL number will be 1000. The CPU Booster is available only in case of perfect gas or real gas without preconditioning. The CPU Booster is not recommended when modelling low speed flows without preconditioning For the turbulence simulations, the CPU Booster is compatible only with the 0-equation and 1-equation turbulence models. The CPU Booster is not compatible with the phase-lagged and NLH simulations. When simulating flow with real gas, the results obtained with CPU Booster may be less accurate if either the allowed temperature range is too large or if the properties are expected to vary significantly in the allowed temperature range. In this case, the results obtained with CPU booster could be different from a computation run without CPU booster. 6-2.2.3 Multigrid Parameters In the left part of the Numerical Model page, three boxes are visible. The first one is an information box, named Grid levels: current/coarsest. It indicates for each of the i, j and k directions the currently selected grid level and the number of the coarsest grid level available in the corresponding direction. The second box of the Numerical Model page is an input box that allows to define the Current grid level for each of the i, j and k directions. • The coarsest grid level depends on the number of times the grid can be coarsened, along each of the (i,j,k) directions. For example, if the grid has 17*33*33 points in the i, j, k directions, it has respectively 16*32*32 cells. The i direction (16 cells) can thus be divided 4 times by 2, while the others can be divided 5 times by 2. The following grid levels are then available: 000 17*33*33 (18,513 points) 111 9*17*17 (2,601 points) 222 5*9*9 (405 points) 333 3*5*5 (75 points) 444 2*3*3 (18 points) 455 2*2*2 (8 points) The coarsest grid level available is then 4 along i and 5 along j and k. • The current grid level is the finest grid level (for each of the i, j and k directions) on which the computation will take place. The selected levels should be in the range between 0 and the coarsest grid level available for each of the i, j and k directions. Referring to the example given just above, the user can do a first run on level 3 3 3 to validate the computational parameters and then switch to level 1 1 1 or 0 0 0 for a finer solution. It gives a high flexibility to the system since with one grid, the user can run simulations on several sub-meshes. All combinations between the i, j and k grid levels, in the specified range, are possible such as 2 3 1 or 0 3 2...etc. It is however not recommended to use such hybrid levels (e.g. 010 or 211) since it deforms the mesh in a preferential direction and thus possibly FINE™/Turbo 6-3 Numerical Scheme Numerical Model increasing the aspect ratio. Consequently, the quality of the resulting mesh can be decreased. Press after each modification to validate the new specified levels. The use of multigrid is highly recommended in order to ensure fast convergence of the flow solver. The mesh used to discretise the space can have multiple grid levels in each direction of the computational domain i, j and k. These levels are numbered from 0 (finest grid) to N (coarsest grid). The grid level (N) available in one direction (I, J, or K) is the smallest grid among all patches on that particular direction (I, J, or K). The third box, named Number of grid level(s), permits to significantly accelerate the convergence to steady state if several grid levels are available: the flow calculation is performed simultaneously on all the grid levels. This technique is referred to as the multigrid strategy. This number should be chosen as high as possible, and deduced from the information displayed on the available grid level and the grid level on which the computation will be performed (Current Grid Level). Finally, the option Coarse Grid Initialization enables, before calculating the flow on the mesh contained in the IGG™ files, to perform a preliminary flow calculations on a coarser mesh automatically created by the flow solver by coarsening the initial one. This provides a rapid estimation of the flow. This technique is referred to Full Multigrid. 6-2.2.4 Preconditioning Parameters This box allows the user to choose the Hakimi or Merkle preconditioners. The parameters are only available when an incompressible fluid is selected on the Fluid Model page or when the Low Speed Flow (M<0.3) option is activated on the Flow Model page. The upwind spatial scheme (Numerical Model page) is not available if the preconditioning option is chosen. a) Hakimi Preconditioning When choosing Hakimi preconditioning, extra parameters have to be defined. The variables that the user controls are reference pressure P ref , reference temperature T ref , β coefficient β∗ and characteristic velocity U ref . P ref and T ref are accessible through the Flow Model page. The default value of β∗ is 3. Based on our experience with the presented low speed preconditioner the parameter β∗ can be taken of order unity for inviscid flow computations. For viscous computations associated with Reynolds numbers greater than about Re=1000, a constant value β∗ of order unity is also adequate. If convergence difficulties are encountered at the very beginning of a computation, it is recommended to increase the value of the parameter β∗. Remember however that a too large value of β∗ will introduce excessive artificial dissipation into the solution. For lower Reynolds number the parameter β∗ has to vary in order to preserve numerical stability and a good convergence rate. The parameter β∗ should increase as the Reynolds number decreases and may vary over several orders of magnitude (see Figure 6.2.2-3). With low Reynolds number, β∗ has to be increased. But this increases the dissipation and therefore alters the precision of the solution. 6-4 FINE™/Turbo Numerical Model Numerical Scheme FIGURE 6.2.2-3 Typical variation of the preconditioning parameter β∗ with Reynolds number U ref is representative of the maximum velocity in the flow field. For example, in external flows, Uref could be taken as the free stream velocity whereas in internal flows it could be taken as the maximum inlet velocity. Note, for the user’s convenience, the constant Uref is always equal to the reference velocity specified in the Flow Model page, which means that one of them (Uref/reference velocity in the Flow Model page) is changed, the other one will be changed automatically. The choice of Uref has an influence on the convergence. Another expert parameter ALPHAP (α) is accessible in the Control Variables page under Expert Mode. According to several computations accomplished with the central scheme, good convergence rates were obtained for values of α lying in the range [-1,1]. So far the best value is found to be α=-1. b) Merkle Preconditioning When choosing the Merkle preconditioner, no extra inputs are required. 6-2.3 Expert Parameters 6-2.3.1 Interfaced Expert Parameters a) Multigrid Strategy If the option Coarse Grid Initialization is activated, the computation starts on the coarsest grid level and includes a finer grid level each time one of the two following criteria is satisfied: • The maximum number of cycles to be performed on each grid level is reached. This parameter is specified through the input box in the Full MultiGrid Parameters area as the Maximum number of cycles per grid level. • The residual on the current grid level has dropped a certain order of magnitude as indicated by the Convergence criteria on each grid level in the Full MultiGrid Parameters area. For the Convergence criteria on each grid level, both the RMS and maximum residuals are checked when passing from one grid level to the next one in full multigrid initialization. The flow solver jumps to the next grid level when both criteria has decreased FINE™/Turbo 6-5 Numerical Scheme Numerical Model e.g. 3 orders of magnitude. • An additional input box permits to select the number of sweeps to be performed on the coarse grid levels through the input box Number of sweeps on successive grid levels. The amount of sweeps is the amount of times the Runge-Kutta operator is applied. In the default configuration of the solver called Linear progression, the number of sweeps on each level equals the level number (2 sweeps on second level,...). It has been observed in many cases that the convergence rate may be significantly improved by performing a higher number of sweeps on the coarsest levels. Recommended sets of values are proposed in the Sweeps area through the parameter Scheme definition: for instance (1,2,16) in case of 3 grid levels. However, it is should be noted that more sweeps have as a consequence more time required for an iteration. b) Spatial Discretization Two types of spatial discretization are available: • central scheme (default) and • upwind scheme. A new way of calculating the artificial dissipation based on the primitive variables can be accessed by switch expert parameter IARTVS to 2 when a central scheme is chosen. Such a new way can limit or remove strong overshoot in temperature in the vicinity of holes when running blade cooling configurations with the source term approach. This method is restricted to non-preconditioned perfect gas and real gas implementations. And it is not applicable with NLH method. If an upwind discretization is chosen, an input box appears in a Spatial discretization parameters area to specify the order of accuracy of the desired upwind scheme: first or second order. See section for more detail on those different schemes. Condensable and preconditioned fluids are not compatible with the use of upwind schemes for space discretization. c) Temporal Discretization The temporal discretization scheme used for the computation is an explicit multi-stage Runge-Kutta scheme. In the interface, the time stepping technique should be selected between Local time stepping (default) and Global time stepping. See section for more detailed information on the temporal discretization. In general the default scheme is recommended. If the computation is an unsteady computation, unsteady parameters box appears. Please refer to chapter section 6-3.1 for a description of those unsteady parameters. 6-6 FINE™/Turbo Numerical Model Numerical Scheme 6-2.3.2 Non-interfaced Expert Parameters Additional parameters related to the numerical model are available in the list on the Control Variables page in Expert Mode. a) Multigrid IMGDIR(integer): Indicates if coarsening will be applied in the specified I, J or K direction (three values): 1 1 1 (default): coarsening applied in all directions 0 0 0: no coarsening applied in all directions 1 1 0: coarsening applied only on I and J directions IPROLO(integer): Indicates the order of the prolongation within the multigrid approach. The default value is depending on the selected fluid type and turbulence model. 0: piecewise constant prolongation, 1: linear prolongation with damping, -1: linear prolongation without damping, 2: linear prolongation except at boundaries(-2). When used with a preconditioned formulation, this damping option is somewhat useless and can be damaging. FINE™/Turbo therefore sets it to off when preconditioning is used. When used with k-ε turbulence model and preconditioning, the linear prolongation with damping is recommended. IRESTR(integer): Gives the order of the restriction operator of the multigrid. = 0 (default): corresponds to linear restriction, = 1: to quadratic restriction. MGRSTR(integer):Applies only for multigrid and fixes the type of multigrid cycle. MGRSTR=1: V-cycle; MGRSTR=2: W-cycle; MGRSTR=3: F-cycle; MGRSTR=4: V-cycle in sawtooth; MGRSTR=5: W-cycle in sawtooth; MGRSTR=6: F-cycle in sawtooth. Default: MGRSTR=1. MGSIMP(integer):Applies only for multigrid. If MGSIMP>1 a simplification will be used on coarser levels. If MGSIMP=1 a more dissipative scheme is used on coarser meshes, i.e. first-order upwind (if 2nd order upwind scheme is used) or central scheme with increased 4th order dissipation on solid walls (if central scheme is used). If MGSIMP=2, in addition to the simplification for MGSIMP=1, viscous and source terms (of turbulence) are neglected on coarser levels. No simplification for MGSIMP=0. Default: MGSIMP=1 RSMPAR(real): Residual smoothing parameter σ*/σ. A value less or equal to zero means no residual smoothing. SMCOR(real): Only used in case of multigrid. SMCOR has the same meaning as RSMPAR but applies to the interpolated multigrid corrections instead of the residuals. SMCOR indicates whether interpolated corrections should be smoothed or not. The default value for SMCOR is 0. b) Spatial Discretization IFACE(integer): FINE™/Turbo = 1(default): Cell face gradients are used for the viscous fluxes, 6-7 Numerical Scheme Numerical Model = 0: cell corner gradients. IWAVVI(integer): Only used if IFACE=0. If IWAVVI=0 the cell face gradients are obtained by arithmetic averaging of the cell corner gradients. If IWAVVI=1 a weighted averaging is used instead, taking the cell volumes into account. IWAVCO(integer): If IWAVCO=0 a variable averaging is performed. If IWAVCO=2 a flux averaging is used instead. c) Central Discretization CDIDTE(real): Constant used in the exponential damping factor that is used in the numerical dissipation for k and ε, both if central or upwind schemes are used. The default value for CDIDTE is 100 EXPMAR(real): Exponent in the multi-dimensional scaling model of Martinelli of the dissipation used in central schemes. Default EXPMAR=0.5 i.e. multi-dimensional scaling not used. IARTV2(integer): Defines whether the second order artificial dissipation switch should be based on both pressure and temperature gradients (parameter IARTV2=1) or on pressure gradients only (IARTV2=0). In the default configuration, only pressure gradients are taken into account. Both pressure and temperature gradients (IARTV2=1) can only be taken into account for compressible cases. VIS2(real): Coefficient κ(2) for 2nd order dissipation in the central scheme (default VIS2=1.0). VIS2KE(real): Used only for k-ε turbulence model. Coefficient κ(2) for 2nd order dissipation in the central scheme, as applied to the k and ε equations. Default VIS2KE=1.0 VIS2SW(integer): This parameter switches off all second order dissipation for incompressible fluids (when set to the default: VIS2SW=1). Second order dissipation is intended for stabilization of the shocks but there are no shocks in incompressible flows. Therefore the default is to switch off all second order dissipation for incompressible fluids. Sometimes it may be stabilizing to use some second order dissipation. In that case set this parameter to zero. VIS4(real): Coefficient κ(4) for 4th order dissipation in the central scheme. Default VIS4=0.1 VIS4KE(real): Used only for k-ε turbulence model. Coefficient κ(4) for 4th order dissipation in the central scheme, as applied to the k and ε equations. Default VIS4KE=0.1 VISNUL(integer): Eliminates 2nd order dissipation fluxes along the physical boundaries (central scheme). Default VISNUL=1. If VISNUL=0, the procedure is not applied. d) Upwind Discretization ENTRFX(real): Entropy coefficients. The first value is the entropy fix coefficient applied to the linear field, the second value is applied to the non-linear field. ENTRFX<1. means a constant value, ENTRFX>1. means scaled with the spectral radius through a factor ENTRFX-1. IRATIO(integer): Vector of two values, that indicate which effective ratio is to be used. The first value applies to the linear field, the second to the non-linear field. IRATIO is only active for second-order upwind schemes. 6-8 FINE™/Turbo Numerical Model Numerical Scheme IROEAV(integer): =1 indicates that Roe averages are to be used to calculate cell face data. If IROEAV=0 (default), arithmetic averaging will be used. e) Time Discretization IBOTH(integer): used in combination with ISWV. The latter parameter indicates whether the dissipation terms are recalculated or not in the different Runge-Kutta stages. IBOTH=0 means that the dissipation term only contains the physical, viscous dissipation; IBOTH=1 means that it also contains the artificial/upwind dissipation. The default value = 2 means that the dissipation term contains only the artificial dissipation. The physical dissipation is computed once per time step. IRKCO(real): Runge-Kutta coefficients. One for each stage, the first one for the first stage, the second one for the 2nd stage and so on. The default values that are used when nothing is set in IRKCO are: 1st order upwind - Van Leer: 4stage .0833 .2069 5stage .0533 .1263 2nd order upwind - Van Leer: 4stage .1084 .2602 5stage .0695 .1602 central scheme - Jameson: 4stage .25 .3333 5 stage .25 .1666 both central and upwind - Eliasson: 4stage .125 .306 5stage .0814 .191 .4265 .2375 1. .4414 1. .5052 .2898 1. .5060 1. .5 .375 1. .5 1. .587 .342 1. .574 1. NSTAGE(integer): number of stages for the explicit Runge-Kutta scheme. In practice, 4 or 5 stage schemes are mostly used. = 4: ISWV = 1 1 0 ...(ISWV can be modified afterwards independently) = 5: ISWV = 1 0 1 0 1 0 ...(ISWV can be modified afterwards independently) IRSMCH(integer): specifies the type of residual/correction smoothing. = 1: standard version = 2 (default only if Hakimi preconditioning): Radespiel & Rossow = 3 (default): Zhu, time step dependent coefficients = 4: Swanson & Turkel viscous = 5: Vatsa. On meshes without high aspect ratio. ISWV(real): governs the recalculation of the dissipative residual in the different RungeKutta stages. A value α between 0 and 1 is allowed. Zero means no recalculation of dissipative residual (latest available value will be used); 1 means recalculation. For intermediate values, a weighted averaging of the latest dissipation residual and of the preceding one is applied with the weight α and (1-α) respectively. E.g. for a 5-stage scheme: ISWV = 1 0 1 0 1, means that the dissipative residual is calculated in 1st,3rd and 5th stage only. ISWV is used in combination with IBOTH. RSMPAR(real): residual smoothing parameter σ*/σ. A value less or equal to zero means no residual smoothing. Default value = 2. FINE™/Turbo 6-9 Numerical Scheme 6-3 Time Configuration Time Configuration To perform time independent computations it is sufficient to select Steady. In case time dependence needs to be included in the simulation Unsteady or Harmonic should be selected which gives access to additional parameters respectively for unsteady flow simulation. All parameters in the FINE™/Turbo interface related to Unsteady computations are described in the following section. The parameters related to Harmonic computations are described in section 8-4. 6-3.1 Interface for Unsteady Computation When selecting Unsteady time configuration in the Flow Model page the following additional parameters become accessible in the FINE™/Turbo interface: a) Rotating Machinery On the Rotating Machinery page, under the Rotor-Stator tab, the Domain Scaling rotor/stator interaction is activated. Furthermore, the Phase Lagged capability can be activated on the top of the page. When activated, the Phase Lagged rotor/stator interaction will be applied. b) Time Dependent Boundary Conditions On the Boundary Conditions page the boundary conditions at inlet and outlet may be defined as a function of time. To define a time dependent boundary condition go to the Boundary Conditions page and change the default (Constant Value) with the pull down menu to: • fct(time) to define a constant value in space but varying in time. Click on the profile data button ( ) to activate the Profile Manager. • fct(space-time) to define a space and time dependent variation of the boundary condition value. In this case a one-dimensional space profile has to be defined. The time profile to impose is a scaling factor that is applied to the space profile. This means that the profile in space is only varying in time with a certain scaling factor. Another way to define an inlet/outlet unsteady boundary condition is to set an absolute rotational speed to the boundary condition by activating Rotating Boundary_Condition and specifying the rotational speed in Rotational Speed Unsteady respectively under the INLET and OUTLET tabs, and to set the periodicity of the signal entered in FINE™/Turbo through the expert parameter NPERBC. The FINE™/Turbo solver allows only one rotation speed (combined with a zero rotation speed) when performing an unsteady simulation using the Domain Scaling method or Phase lagged method. The inlet/outlet unsteady boundary condition circumferential profile has to be imposed on a range covering the initial blade passage location and the blade passage location after one period of the signal. 6-10 FINE™/Turbo Time Configuration Numerical Scheme Example: T 0 θ1 θ2 π θ3 2π θ4 θ v2.2 t0 FIGURE 6.3.1-4 t0+T Circumferential signal The blade channel is initially (t0) located at θ1,θ2 and will after one period of the signal (T) be located at θ3,θ4. Τhe circumferential signal has thus to be imposed from at least θ1 to θ4. When Rotating Boundary Condition is activated, the time step is no longer specified by the physical time step in the FINE™/Turbo interface in the Computation Steering/Control Variables page. Instead the time step is imposed by defining the Number Of Angular Positions. c) Phase Lagged When activating Rotating Boundary Condition in the Boundary Conditions page to rotate the reference system of the boundary condition at the inlet and/or outlet, the period of the boundary condition should be compared to the blade passing period. In the case of a single blade row calculation with the period of the varying inlet or outlet boundary conditions different from the blade passing period, the Phase Lagged option should be activated in the Rotating Machinery page and the periodicity of the signal entered in FINE™/Turbo has to be specified through the expert parameter NPERBC. The current implementation of the phase-lagged boundary conditions only allows matching and full non matching periodic boundary conditions. This option can be used with non matching periodic boundary conditions (PERNMB) if they are automatically transformed into full non matching boundary by setting the expert parameter IFNMB to 1. d) Control Variables On the Computation Steering/Control Variables page the following parameters appear when selecting an unsteady time configuration non-turbomachine: • Physical Time Step: in general cases the user specifies the magnitude of the physical time step in seconds. This time step is constant through the whole calculation. In cases of turbomachinery applications where Rotor/Stator interfaces are detected or Rotating Boundary Condition activated, the Number Of Angular Positions is requested instead of the time step as described in section 6-3.3.4. FINE™/Turbo 6-11 Numerical Scheme Time Configuration • Number Of Physical Time Steps: to define the number of time steps to perform. In cases of turbomachinery applications where Rotor/Stator interfaces are detected or Rotating Boundary Condition activated, the Number of Periods can also be specified. • Save Solution Every: allows to save the solution after a constant number of time steps. By default the output files will be overwritten, every time the solution is saved. In order to keep the successive unsteady solutions, the multiple output (Multiple Files) option has to be activated. • Include Time Averaged Solution in Output: When activated the time averaged solution will be saved in a "_tav.cfv" file. This option is only available when Rotor/Stator interfaces are detected or the Rotating Boundary Condition is activated. The option Include Time Averaged Solution in Output is not available when the phase lagged approach is used. A tool has been provided, which allows the user to compute the time averaged solution for the phase lagged computation. For more information, refer to Chapter 6-3.3.6. • Outputs For Visualization: — At end only and Intermediate Restart Files: One File: During the computation, one set of output files is saved1 for a possible restart of the unsteady computation. Output files for visualization in CFView™ are only available at the end of the computation. No second order restart possible. — At end only and Intermediate Restart Files: Multiple Files: During the computation, multiple sets of output files are saved1 for restart of the unsteady computation. Output files for visualization in CFView™ are only saved at the end of the computation. This option allows a second order restart (see paragraph e). — Intermediate and One Output File: One set of output files is saved2 for restart of the unsteady computation and visualization in CFView™ during the computation. No second order restart possible. — Intermediate and Multiple Files: Multiple sets of output files are saved2 for restart of the unsteady computation. and visualization in CFView™ during the computation. This option allows a second order restart (see paragraph e). This combination has to be chosen to be able to make an animation of the saved time steps in CFView™. • Number Of Steady Iterations: the number of iterations to initialize the unsteady computation. Such initialisation is performed with the steady state algorithm, using fixed geometry and mesh as well as constant inlet/outlet boundary conditions. In case this initialisation procedure is used the steady state iterations can even be proceeded by a full multigrid process allowing a rapid initialisation of the flow. • Save Steady Solution Every: the number of iterations at which the solution of steady initialisation is saved By default only one output file is created. For the generation of multiple output files, the Multiple Files option has to be selected. 1. The solution is saved every x time steps as specified in Save Solution Every ... time steps 2. The solution is saved every x time steps as specified in Save Solution Every ... time steps 6-12 FINE™/Turbo Time Configuration Numerical Scheme e) Second Order Accurate in Time The FINE™/Turbo solver performs second order accurate simulations in time. In order to allow a second order restart it is necessary to select Multiple Files in the Computation Steering/Control Variables page. When Multiple Files option is selected, in unsteady calculations the ".cfv" and ".cgns" are saved at the requested time steps and only a part of the ".cgns" file is saved for the previous time step. When requesting a restart of an unsteady computation the FINE™/Turbo solver will automatically find this second solution file to use. If this file is not found, a first order scheme is used for the first time step. Note that only a limited output is saved when selecting Multiple Files with Output For Visualization/At end only. If a solution is requested every x time steps, only solution files with extension ".cgns" are written every x time steps instead of a full set of solution files. This limited output still allows to restart from this solution (see section 122). The full set of solution files will be written at the end of the computation. 6-3.2 Expert Parameters for Unsteady Computations 6-3.2.1 Numerical Model in Expert User Mode On the Numerical Model page, two new parameters appear in the user expert mode when selecting the Dual time stepping technique. They are the control variables for the inner iterations. For each physical time step a certain amount of iterations is performed in pseudo time leading to a converged solution independent of the pseudo time. • Convergence criteria of the inner iterations (orders of magnitude of reduction). The inner iterations are stopped if the reduction of the residuals reaches the specified value. • Maximum number of inner iterations: it allows to define the maximum number of iterations to perform for each time step. In general the default of 100 iterations per time step is sufficient. The inner iteration process is automatically stopped after this maximum number of iterations if the convergence criteria has not been satisfied before. 6-3.2.2 List of Non-interfaced Expert Parameters The following expert parameter related to unsteady computations are accessible on the Control Variables page by selecting the Expert Mode. ICYOUT(integer): can be equal to 0 or 1 (default): 0: name of output changes with suffix _t#iter, 1(default): each solution is overwritten every cycle. IFNMB(integer): can be equal to 0 (default) or 1: 0 (default): to keep all PERNM or NMB boundaries, 1: to transform all PERNM boundaries into periodic full non matching ones or all NMB boundaries into full non matching ones. NPERBC(integer): can be equal to 1 (default) or integer value: 1 (default): when the inlet/outlet unsteady boundary condition is a rotating circumferential profile (activating Rotating Boundary Condition and specifying the rotational speed in Rotational Speed Unsteady respectively under the INLET and OUTLET tabs) and the boundary condition is entered in the FINE™/Turbo interface for the full range [0,2π]. FINE™/Turbo 6-13 Numerical Scheme Time Configuration N: when the inlet/outlet unsteady boundary condition is a rotating circumferential profile (activating Rotating Boundary Condition and specifying the rotational speed in Rotational Speed Unsteady respectively under the INLET and OUTLET tabs) and the boundary condition is entered in the FINE™/Turbo interface for part of the range [0,2π/N] covering one or multiple periods of the signal. RELPHL(real): 6-3.3 0.5 (default) if necessary, under-relaxation factor can be applied on Periodic and R/S boundary conditions by reducing the two values of the expert parameter for respectively the periodic and the R/S boundary conditions. Best Practice on Time Accurate Computations To perform time accurate computations, general advice is provided in this section. For advice on how to perform a time accurate turbomachinery calculation including rotor/stator interactions see section 8-3.2.3. 6-3.3.1 General Project Set-up for Time Accurate Computations 1. Create a new project, 2. Select the fluid to use in the Fluid Model page, 3. Select Unsteady time configuration in the Flow Model page and set all the other parameters on this page in the same way as for a steady computations as detailed in section 4-2 and section 43. 4. On the Rotating Machinery page set all the parameters (Phase Lagged option) in the same way as for a steady computation as described in Chapter 8. 5. Set the steady or unsteady boundary conditions. For more detail on time dependent boundary conditions and phase lagged approach see section 6-3.3.2. 6. Concerning the initial solution for unsteady computations there are three possibilities: — to start from a steady solution, — to start from an unsteady solution, — to use constant values, initial solution for turbomachinery or throughflow as an initial guess with or without steady state initialisation. For more detail on these initialisation procedures see section 6-3.3.3. 7. All outputs available in steady mode are also available in unsteady mode (see Chapter 10). 8. On the Control Variables page set: — the physical time step or number of angular position (see section 6-3.3.4) and the number of time steps or periods, — the amount of output files (see section 6-3.3.5), — amount of iterations in steady state initialisation (see section 6-3.3.3). 6-3.3.2 Time Dependent Boundary Conditions Unsteadiness can be generated by means of time varying inlet/outlet boundary conditions. Two different situations can be encountered: 6-14 1. The time variation is imposed as an amplitude factor of the space variation, 2. The time variation is imposed by rotating the inlet and/or outlet boundary condition. The absolute rotation speed of the boundary condition(s) is imposed in the Boundary Conditions page. FINE™/Turbo Time Configuration Numerical Scheme Depending on the periodicity of the boundary condition the phase lagged approach needs to be used: 1. The circumferential distribution of the imposed inlet/outlet conditions has the same period as the blade row. The calculation of such time-dependent flow does not require to activate the Phase Lagged approach. 2. The period of the time varying inlet/outlet boundary condition is different from the blade passing period. The calculation of such time-dependent flow requires to activate the Phase Lagged approach at the top of the Rotating Machinery page. A circumferential profile must be entered in the FINE™/Turbo interface for the full range [0,2π] and NPERBC = 1 or for part of the range [0,2π/N] covering one or multiple periods of the signal and NPERBC = N. The profile should be based on θ, z-θ or r-θ. The profile is rotating at the speed, specified in the Boundary Conditions page (Rotational Speed Unsteady). It is important that the inlet/outlet unsteady boundary condition circumferential profile is imposed on a range covering the initial blade passage location and the blade passage location after one period of the signal (see Figure 6.3.1-4). 6-3.3.3 Initialisation Procedure a) Start From Steady Solution In most cases, it is first required to perform a preliminary steady state computation. The objective might be to ensure that the problem naturally depicts the unsteady behaviour and/or to get an adequate guess solution before going towards time accurate calculations depicting periodic behaviours. The steady state initialisation may be done in a separate computation, performed in steady mode using the time-marching approach based on a local time stepping, which is proposed by default. The time accurate calculation is then started using this solution as an initial solution. To set up the time accurate calculation in this case follow the steps 1 to 8 as detailed in section 6-3.3.1. In step 6 select in the Initial Solution page from file and select the solution of the steady computation. In step 8 (section 6-3.3.1) it is also possible to select additional steady state initialisation in the Control Variables page (see paragraph c). b) Start From Time Accurate Solution It is possible to start from a previously performed time accurate solution. For general information about starting from an initial solution see section 9-4. In order to allow to do a second order accurate restart it is necessary that Multiple Files option is selected in the Control Variables page in the Output Files parameters. When the option is activated in unsteady calculations the ".cfv" and ".cgns" files are saved at the requested time steps and only a part of the ".cgns" file is saved for the previous time step. When requesting a restart of an unsteady computation the FINE™/Turbo solver will automatically find this second solution file to use. If this file is not found, a first order scheme is used for the first time step. c) Steady State Initialisation in Unsteady Computation The steady state initialisation is automatically performed before starting the time accurate computation (that means within the same computation). To perform a steady state initialisation in an unsteady computation, the number of iterations has to be entered in Steady Initialisation parameters on the Control Variables page. FINE™/Turbo 6-15 Numerical Scheme Time Configuration 6-3.3.4 Physical Time Step The physical time step should be entered on the Control Variables page. The time step to choose depends on the expected frequency of the flow phenomena to capture. In general it is recommended to compute at least 10 to 20 time steps per period. When working with the Domain Scaling method, using a Number Of Angular Positions of 10 points per blade passage is giving a coarse but reasonable result. To have a more accurate (but more CPU consuming) result choose 20 to 30 points per passage (see Chapter 8-3.2.3 for more details). When working with the Phase Lagged method, the Number Of Angular Positions is the number of time iterations per 2π (see Chapter 8-3.2.4 for more details). The following examples show the settings of Number Of Angular Positions and Number Of Time Steps when using an unsteady inlet boundary condition. Example 1: single blade row calculation involving phase-lagged boundary conditions When working with a N1 blades turbomachine and a periodic signal at inlet presenting a periodicity of N2 and plotted on [0,2π/N2] range. • Number Of Angular Positions = i x N1 where i is an integer imposed so that (i x N1) is around 30. • Number Of Time Steps = j x (Number Of Angular Positions) where j is the number of full revolutions. Usually j is set to 20. • NPERBC = period of the signal (N2) (Number Of Angular Positions)x(NPERBC) corresponds to the number of time steps per full revolution (2π) Example 2: complete row calculation involving sliding boundary conditions When working with a N1 blades turbomachine and a periodic signal at inlet presenting a period of N2 and plotted on [0,2π] range. • Number Of Angular Positions = i x N1 x N2 where i is an integer so that (i x N1) and (i x N2) are around 30. • Number Of Time Steps = j x (Number Of Angular Positions) where j is the number of full revolutions. Usually j is set to 20. • NPERBC = 1 (Number Of Angular Positions)x(NPERBC) corresponds to the number of time steps per full revolution (2π) 6-3.3.5 Amount of Output By default only one set of output files is created, which is periodically overwritten. Activate Multiple Files in the Control Variables page to create a set of output files for each time step that an output will occur (this depends on the Save solution Every entry available in the Control Variables page). ".cgns" files will be generated. The files are automatically renamed accordingly to the time step computed using the suffix "_t#." that is thus determining the #th physical time step. The corresponding ".cfv" files can be read in CFView™ only if in addition of the Multiple Files the Intermediate option has been selected in the Output For Visualiza- 6-16 FINE™/Turbo Time Configuration Numerical Scheme tion option. Note that the ".run" and ".cgns" files (without "_t#." suffix) are linked to the initial state of calculation. 6-3.3.6 Time Averaged Solution For domain scaling simulations, the user can get a time averaged solution by activating the option Include Time Averaged Solution in Output on the interface. But for phase lagged simulations, this is not the case. A tool plg2harmo is provided in the FINE™/Turbo package. Using plg2harmo, the user can compute a time averaged solution from the solutions obtained by the phase lagged simulation or the domain scaling simulation. The tool plg2harmo can only be launched from the shell. On Linux: plg2harmo project-path/project-name.run On Windows: Installation path\bin\plg2harmo.exe project-path/project-name.run (for 32bits OS) Installation path\bin64\plg2harmox86_64.exe project-path/project-name.run (for 64bits OS) Then two new files "project-name_ft0.run" and "project-name_ft0.cgns" will be generated. The two files include the time averaged solution. The user can load these files into CFView™ for postprocessing. If the periodicity of the different rows is different, the number of the solution files must be larger than the smallest periodicity. The treatment of solid data is not allowed. The calculation of time-averaged velocities for a computation with an inlet or outlet distortion set as boundary condition is not allowed. FINE™/Turbo 6-17 Numerical Scheme 6-18 Time Configuration FINE™/Turbo CHAPTER 7: 7-1 Physical Models Overview FINE™/Turbo contains the following physical models: • Fluid-Particle Interaction to model solid particles in the flow. • Fluid-Structure to model the fluid structure interaction. • Passive Tracers allows to introduce species that are entrained by the flow, without influencing its properties. • Porous Media Model to model the flow in porous media • Cavitation Model to model cavitating flow Each of these models requires a special license feature. If the model is not accessible due to a missing license it is displayed in grey. Please contact our local sales or support office for more information about the possibility to obtain a license. 7-2 Fluid-Particle Interaction 7-2.1 Introduction Particle-laden flows cover a large class of two-phase flows, such as droplets or solid particles in a gas or liquid flow, or bubbles in liquids. One phase is assumed to be continuous and occupies the majority of the flow. It is called the "carrier" phase. Another phase, whose volume fraction is relatively small (usually less than 10-2), exists as a number of separate elements or particles. It is called the "dispersed" phase. In this section 7-2 an overview is given of the fluid particle interaction module incorporated in FINE™/Turbo GUI: • 7-2.2 describes the main functionalities of the module and the way to proceed in the FINE™/ Turbo interface. FINE™/Turbo 7-1 Physical Models Fluid-Particle Interaction 7-2.1.1 Lagrangian Approach A Lagrangian approach is used here, whereby the trajectories of individual groups of particles are calculated as transported by the velocity field of the carrier phase, including the effect of drag and other forces. The calculations of the carrier flow and of the particles can be fully coupled, the fully coupling approach implying that the calculation of the particles trajectories is followed by a second flow calculation, taking into account the presence of the particles in the flow (the interphase forces are introduced as source terms in the flow calculation). The sequence consisting of a flow calculation and of the particle traces tracking can be repeated several times until no changes are observed in the results (usually 3 to 10 times). In the present Lagrangian model, the motion of the particles is only influenced by their own inertia and by the flow, i.e. the local aerodynamic or hydrodynamic forces. Interactions between the particles are currently not considered. This implies the hypothesis of a dilute flow. On the contrary in a dense flow, particle motion is governed by their direct interaction, which implies more complex models, such as the Eulerian ones, in which both phases are modelled as continuous phases. Particle-laden flows are found in many industrial applications such as cyclone separators, pneumatic transport of powder, droplet and coal combustion system, spray drying and cooling or sandblasting. In all cases, the flow consists of a continuous phase - also named carrier flow - and a dispersed phase in the form of solid particles, liquid droplets or gas bubbles. In general, the motions of the carrier flow and of the dispersed phase are interdependent. In the lagrangian approach, the physical particle cloud is represented by a finite number of computational particles. The continuous phase (fluid) is treated as a continuum using a boundary-controlled method whereas the dispersed phase (particles) is treated as a number of separate particles. The particles are successively tracked as a single probe particle through the flow field using a Lagrangian formulation. In the case of laminar flows, each particle will follow a unique deterministic trajectory. In the case of turbulent flows however, particles will have their own random path due to interactions with the fluctuating turbulent velocity field. This feature is taken into account in the FINE™/Turbo solver through a stochastic treatment. This approach consists of employing a sampling technique based on a Gaussian probability density function to introduce the random nature of the turbulent velocity field. The particle diffusion due to turbulence can therefore be modelled without introducing artificial diffusion properties of the cloud. According to the distribution and contents of the particles, an averaging procedure provides phase coupling source terms to be added into the Eulerian carrier phase conservation equations. The twoway coupling can be achieved through global iterations. 7-2.1.2 Algorithm The hypothesis of a dilute mixture permits to have a very simple sequential calculation of the trajectories of the different particles injected through the inlet sections. The algorithm considers successively the different inlet patches. The user specifies the number of trajectories per cell. The origins can be located at a given point chosen by the user, or equally distributed throughout the cell. The algorithm proceeds cell by cell, the time step being calculated so that several time steps are performed in each mesh cell. The procedure starts at a cell of an inlet boundary and stops when a boundary is reached. Each time step consists of: • the calculation of the force on the particle. • the integration to find the new velocity and position. 7-2 FINE™/Turbo Fluid-Particle Interaction Physical Models • the determination of the cell in which the particle is located. 7-2.2 Fluid-Particle Interaction in the FINE™/Turbo GUI To access the parameters select the Fluid-Particle Interaction page under the Optional Models. In the parameters section click on Fluid-particle calculation to activate this model (see Figure 7.2.2-1). The user enters not only the main features of the numerical simulations but also the characteristics (i.e. processes to be taken into account) of the interphase force between the fluid and the particles. 7-2.2.1 Parameters The top window allows to choose the degree of influence of the particles on the flow. The calculation of the carrier flow and of the particles can be fully (2-way coupling) or weakly (1-way coupling) coupled: • in the 1-way coupling approach the flow calculation (ignoring the influence of the particles on the flow field) is followed by a calculation of the trajectories of particles. In this case, there is no influence of the particles on the flow. • in the 2-way coupling approach the calculation of the trajectories of particles is followed by a second flow calculation, taking into account the presence of the particles in the flow (the interphase forces are introduced as source terms in the flow calculation). The sequence can be repeated several times (by entering the Number of global iterations) until no changes are observed in the results (usually 3 to 10 times). Concerning the simulation itself, the user can choose the Global strategy: • Start from scratch: to start the flow calculations and then pursue with the particle tracking simulation. In this particular case, the criterion for the carrier flow calculations convergence is the one set on the Control Variables page (set to -6 by default). • Start from converged flow solution: to proceed directly with the Lagrangian coupling from a previous converged flow calculation. FIGURE 7.2.2-1 Parameters page of the lagrangian fluid-particle interaction model. The usual way to proceed is: 1. FINE™/Turbo perform a pure flow study without activating the Fluid-Particle Interaction model in a computation. 7-3 Physical Models Fluid-Particle Interaction 2. while this computation is active in the list of Computations subpanel on the top left of the interface create a new project by clicking on the New button. 3. in this new computation activate the Lagrangian Fluid-particle calculation and perform a computation with Lagrangian coupling. The particles encounter several forces: the friction force, i.e. the resultant of the pressure and viscous stress in the carrier phase over the particle surface, as well as potential inertia and gravity forces. The user is free to introduce the Gravity Forces through the vectorial components of the acceleration of gravity on the Flow Model page. An inertial force due to the rotation of the system of reference can also be included. If some of the blocks are rotating the option Body forces/Rotation of reference system should systematically be activated. In this case the reference rotation velocity is the one specified on the Rotating Machinery page. 4. while moving through a turbulent flow, each particle faces a sequence of random turbulent eddies that result in a lack of accuracy in particle velocity and position. This process is taken into account using a stochastic treatment when activating Turbulence. The treatment is available when the k-ε turbulence model is assumed for the carrier flow simulation. In this case a Coefficient for eddy life time has to be imposed. The turbulence is only taken into account for the k-ε turbulence models and for the v2f turbulence model. It is not compatible with the Spalart-Allmaras and SST turbulence models. In the particular case of the Baldwin-Lomax model, turbulence does not have a direct influence on the particles trajectories. 7-2.2.2 Boundary Conditions All boundary conditions available for the carrier flow solver are also accepted by the particle tracking algorithm. The only boundary conditions requiring user’s input are: inlet and solid boundary. The boundary conditions are imposed by selecting a patch on which to fix the condition. The user has to confirm the entered values by clicking on the Apply to selection button (Figure 7.2.2-2). In the list of patches it is not possible to group patches but multiple patches can be selected at the same time to apply the same boundary conditions to all of them. To select multiple patches hold the key while selecting them. a) Inlet Boundary The user can enter a number of classes of particles, each class representing a different type of particles. For each class the inlet boundary conditions have to be specified. The displayed boundary conditions are the one for the class specified in the bar as indicated (a) in Figure 7.2.2-2. To select another class use the scroll buttons on both sides of this bar. The purpose of this is to be able to simulate the presence of different types of particles in the same patch. Note however that multiple classes are of interest for fully couples calculations only, by allowing the flow calculation to account for the presence of different particle types. In the case of a weak coupling strategy it is recommended to create one computation per particle class, because only one particle class can be visualized in CFView™. The expert parameter (in Expert Mode on the Control Variables page) CLASID permits to specify which particle class must be included in the CFView™ output. 7-4 FINE™/Turbo Fluid-Particle Interaction Physical Models (a) FIGURE 7.2.2-2 Inlet boundary conditions for the fluid-particle interaction model The inlet boundary conditions are the following: • spatial distribution of the injection points: uniform over the chosen patch or located at a chosen point of coordinates (x,y,z). • inlet velocity of the particles (absolute or relative frame of reference). The velocity is always considered in the same relative frame of reference as the one of the block in which the inlet particle is located. The relative velocities here defined as the difference between the particle and the flow velocity (a zero relative velocity is therefore very commonly used) whereas the absolute velocity boundary conditions is used when the velocity of the particle is well known and different from the velocity of the flow. Note that only the Cartesian coordinate system is available. • density and mean diameter of the particles. • particle concentration (number of particles/m3). • number of particles per cell should be seen as the number of trajectories per cell. The use of multiple trajectories per cell permits to ensure a more uniform covering of the inlet (and hence of the computational domain) by the particles. This is only of interest in the case of fully coupled calculations where it is important to ensure that the source terms are correctly evaluated in all mesh cells. The use of multiple trajectories does not modify the number of particles entering the domain. Each trajectory must be seen as an ensemble of particles. It is also very often referred to as a computational particle. In the case of full coupling, the number of particles per cell should be statistically large enough to provide accurate averaging of the dispersed phase parameters. Therefore it is recommended in this case to have a high number of particles per cell. This increases the computational time required for the particle tracking process, but gives rise to a smoother distribution of the particles in the domain. In the case of a weak (1-way) coupling, only one particle per cell is usually enough to provide a sufficiently detailed description of the particles distribution in the field. b) Solid Wall Boundary The solid wall boundary condition requires an additional input data, which is the reflection ratio. If the ratio is zero, all the particles remain stuck on the wall, whereas if it is 1.0, all particles are FINE™/Turbo 7-5 Physical Models Fluid-Particle Interaction reflected, without any loss of mass or energy. The user can choose the reflection ratio by clicking on the corresponding button while moving the mouse (Figure 7.2.2-3). Two reflection modes are available and can be selected by the expert parameter IBOUND: • In the default mode (IBOUND = 1) the particle loses a fraction of its mass and hence of its kinetic energy at each wall hit. After several wall hits, the size of the particles becomes very small, and the tracking stops (once the diameter has reached a given ratio of the initial one, specified by the expert parameter DIAMR). • In the other mode (IBOUND = 2) the velocity of the particle is reduced, with an unchanged mass. The particle is stopped as soon as the velocity becomes too small (also specified by the parameter DIAMR). FIGURE 7.2.2-3 Solid boundary conditions for the fluid-particle interaction model 7-2.2.3 Outputs FIGURE 7.2.2-4 Outputs of the fluid-particle interaction model The following quantities are calculated by the solver: 7-6 FINE™/Turbo Fluid-Particle Interaction Physical Models • the number concentration Ni ⁄ Ω where Ni is the number of particles of class i in the cell i of volume Ω, • the mass concentration ρ ipart Ni Ω ipart ⁄ Ω (mass of particles per cell volume) where i ρ ipart is the density of the particle of class i and volume Ω ipart , • the volume concentration N i Ω ipart ⁄ Ω (volume of particles per cell volume), i • the components of the mass weighted absolute velocity vector ( vx , vy , vz ) v x = v xi ρ ipart Ω ipart N i ⁄ ρ ipart Ω ipart N i , i i • the weighted mass and weighted absolute or relative velocity vectors number, • the components of the interphase force F = Fi N i ⁄ Ω . i The solver automatically writes an output file (".tr" and ".tr.sum") containing the particle traces that is read by the CFView™ post processing software. 7-2.3 Specific Output This section describes the specific outputs generated by the Lagrangian module. 7-2.3.1 Field Quantities (’.cgns’) The solver automatically includes in the CFView™ output (".cgns") of the project the field quantities that have been specified by the user under the Outputs tab in the Fluid-Particle Interaction page. These quantities can be scalars or vectors, and are the following: • Vectors Mass-weighted relative velocity (1) Number-weighted relative velocity (2) Mass-weighted absolute velocity (3) Number-weighted absolute velocity (4) Interphase force vector (5) • Scalars Number concentration (51) Mass of particles per cell volume (52) Volume of particles per cell volume (53) Presence (1) or absence (0) of particles in cells (54) Vx: x-component of mass-weighted velocity vector (55) Vy: y-component of mass-weighted velocity vector (56) Vz: z-component of mass-weighted velocity vector (57) Fx: x-component of interphase force (58) Fy: y-component of interphase force (59) Fz: z-component of interphase force (60) FINE™/Turbo 7-7 Physical Models Fluid-Particle Interaction 7-2.3.2 Particles Traces (’.tr’) The solver also creates an specific lagrangian output file (".tr"), containing the trajectories of the all the particles. This file is automatically transmitted to CFView™, which allows for the visualization of the trajectories. 7-2.3.3 Summary File (’.tr.sum’) In addition to the previous outputs, a summary file (".tr.sum") is automatically written by the solver, giving for each injection patch the particles numbers and mass flows through the inlet/outlet boundaries, and the number of particles that remain stuck on the walls. 7-2.4 Expert Parameters Other parameters appear in the Expert Mode of the Fluid-Particle Interaction page under the Parameters tab: • The maximum residence time (TMAX in corresponding ".run" file), which is the time limitation for particle residence in the flow. It may be used either to prevent particle stopping or to avoid an infinite loop, having for instance a particle captured in a separation bubble. After the time has expired, the particle disappears. • The governing equations for particles in a carrier flow consist of a set of non-linear ordinary equations. Two methods are provided to integrate this equations with respect to time (that can be selected in expert mode): — The Runge-Kutta scheme, in which the transfer to the next time level is fulfilled through a finite number of intermediate steps. A two-stage and a four-stage option (NRKS in corresponding ".run" file) are available. This scheme is limited to big particles. — The exponential scheme that lies on a semi-analytical method. This scheme is particularly suitable for small particles. • The Drag force is in general the only considered part of the interphase force. It corresponds to the force on a particle moving in a still fluid at constant velocity (or using the particle reference system, a fixed particle in a uniform laminar flow). At extremely low Reynolds numbers (Rep << 1 i.e. at low relative velocities), it is expressed through the Stokes formula. For higher Reynolds numbers, an optional standard curve fit may be chosen. The choice between the two types of forces can be made in expert mode. Other parameters have a standard value, which may be modified only on rare occasions. They are accessible in the Expert Mode of the Computation Steering/Control Variables page: CLASID (integer): selection of class for CFView™ output 7-8 FINE™/Turbo Fluid-Structure Physical Models LMAX (integer): the maximum number of segments along a trajectory may be used to avoid an infinite loop in the case of an oscillatory movement for instance. DDIMAX (real): tolerance factor to establish that a particle has left a cell (default=1.E-4). I2DLAG (integer): simplification for 2D problems (0 if 3D, 1 if 2D). DIAMR (real): diameter ratio under which the particle tracking process stops (default value: 0.1). KOUTPT (integer):enables to write the ASCII ".tr.out" file containing the output of the trajectories (default value: 0). Please contact our local support office to have more details on this file. 7-3 Fluid-Structure Multi-physics problems, including Fluid-Structure Interaction (FSI), are becoming more important for industrial applications. FINE™/Turbo has integrated several modules, which allows the user to perform multi-physics simulations, including thermal and mechanical simulations. 7-3.1 Thermal 7-3.1.1 Conjugate Heat Transfer a) Introduction The conjugate heat transfer model allows the simulation of the thermal coupling between a fluid flow and the surrounding solid bodies, i.e. the simultaneous calculation of the flow and of the temperature distribution within the solid bodies. The model has been validated for steady state applications. It assumes that some of the blocks of the multiblock mesh are "solid", whereas the other ones are "fluid". The connections between the solid and fluid blocks become "thermal connections" along which the fluid-solid coupling is performed. Conjugate heat transfer is not compatible with Euler simulations. b) Conjugate Heat Transfer in the FINE™/Turbo GUI The Conjugate Heat Transfer model can be activated from the Optional Models / Fluid Structure page under the Thermal tab. When opening the Conjugate Heat Transfer page it looks like Figure 7.3.1-5. All blocks in the mesh are listed on the left of the page and all of them are by default set as "fluid". FINE™/Turbo 7-9 Physical Models Fluid-Structure FIGURE 7.3.1-5 Conjugate Heat Transfer page The only action required from the user to set up a computation involving the Conjugate Heat Transfer model can be decomposed in three steps: 1. determine the "solid" and "fluid" blocks. 2. set the global parameters. 3. define the thermal connections. Those steps are described in the following paragraphs in more detail. b.1) Step 1: Determine Solid & Fluid Blocks The use of the Conjugate Heat Transfer model requires the generation of a multi-block mesh, the "solid" and "fluid" parts of the domain being discretised with separate blocks. Once the mesh is generated, the first step consists in pointing the "fluid" and the "solid" blocks via the FINE™/Turbo user interface. In the default configuration of the solver all blocks are of Fluid type, so that the Conjugate Heat Transfer page does not need to be entered for a classical flow calculation. The transfer of some of the blocks from "fluid" to "solid" is performed by selecting those blocks on the left part of the window and by selecting the option Solid. For each solid block the thermal conductivity has to be specified (in W/m/K). The specified conductivity can be a constant or a profile, seeing Appendix A-5.3 on how to define a profile. The specified value has to be larger than 0. When the automatic grouping based on the Grid Configuration is used, the blocks 7-10 FINE™/Turbo Fluid-Structure Physical Models put as solid during the mesh generation, will automatically be set to solid in the FINE™/ Turbo GUI. b.2) Step 2: Setting Global Parameters The only global parameter is the CFL number used for the time integration of the conduction equation. It can be different from the one used for the fluid. The default value is 1.0. b.3) Step 3: Setting Thermal Connections Once some blocks of the multi-block mesh are set as "solid" blocks, the connections between solid and fluid blocks become "thermal connections". These connections are solid wall boundary conditions with a particular thermal condition, along which the imposed temperature profile is iteratively recalculated in order to ensure a correct coupling. These patches appear in the list of patches in the tab page Solid in the Boundary Conditions page. Although the thermal aspect is fully controlled by the coupling procedure, the kinematic boundary condition must be specified by the user (rotation speed in [RPM]). Type of Connections Between Solid and Fluid Blocks Two types of thermal connections are allowed: • matching connections (one patch on each side), • full non-matching connections (one patch or one group of patches on each side). The connection algorithm is implemented in a general way, allowing on both sides a grouping of solid and fluid patches. This is useful for instance in order to facilitate the coupling of a turbine block with holes with the external flow. One single connection can be built, with on the inner side a group of patches including the blade surface and the outer face of the holes. Type of Connections Between Solid and Solid Blocks Three types of thermal connections are allowed: • matching connections (one patch on each side), • Periodic connections (PER), • full non-matching connections (one patch or one group of patches on each side). The connection algorithm is implemented in a general way, allowing on both sides a grouping of solid and solid patches. 7-3.1.2 MpCCI Coupling a) Introduction For multi-physics problems, many commercial codes, such as FINE™/Turbo and Abaqus etc., can be used to solve only one aspect of the physical problem. One way to perform the multi-physics simulations is to use two or more dedicated codes coupled through the exchange of data. MpCCI (Mesh-based parallel Code Coupling Interface) is a coupling interface developed by the Fraunhofer Institute (SCAI) and used to perform multi-physics simulations. It consists in a server, which handles physical quantities exchanges between two or more heterogeneous solvers (for example a Computational Fluid Dynamics solver and a solid mechanics solver). FINE™/Turbo includes a MpCCI code adapter in order to solve the thermal coupling problems. The adapter takes in charge all communication processes with the MpCCI coupling server. About the settings in MpCCI, please refer to the MpCCI manual. FINE™/Turbo 7-11 Physical Models Fluid-Structure The limitations on coupling with MpCCI are as follows: • Wall heat flux exchange is not compatible with FNMB and condensable fluids. • Not compatible with coarse grid initialization and steady initialization. • Not compatible with NLH. Simulations coupling with MpCCI is available on the following platforms: AIX5.3 64bits, Linux 64bits and Windows 32/64bits. MpCCI v4 is supported b) Thermal Coupling with MpCCI In order to perform a thermal coupling simulation, the user has to select the option MpCCI on the Optional Models/ Flow Structure page under the tab Thermal. All solid patches and groups in the mesh are listed on the left of the page, see Figure 7.3.1-6. The user has to select the coupled surfaces and mark them as "Coupled". The coupled patches must be set as Temperature Imposed on the Boundary Conditions / Solid page. The imposed temperature will be the initial value. FIGURE 7.3.1-6 The thermal coupling with MpCCI c) Expert Parameters The expert parameters related to the thermal coupling with MpCCI: 7-12 ITCPL(integer): defines the number of iterations between each exchange with the coupled code for steady computation. CPLREL(real): relaxation factor for received temperature. This parameter can be useful for steady calculation by reducing it to less than one if computation diverges. For unsteady computation, it should not be modified. FINE™/Turbo Fluid-Structure 7-3.2 Physical Models Mechanical 7-3.2.1 Rigid Motion a) Introduction The predefined Rigid Motion model allows to simulate the flow in a domain where the solid boundary can move. The computation will be unsteady if the boundary is moving in time and steady if the movement is constant in the relative frame of reference. This functionality is compatible with all the existing fluid models and turbulence models. For the mesh deformation, the user can only select the Laplacian smoothing method (in Expert mode). For more information on the Laplacian smoothing and its limitations, please refer to Chapter 7-3.2.4. The main solver limitations with respect to the rigid motion model are as follows: • Not compatible with spatial upwind scheme; • Not compatible with NLH. b) Rigid Motion in the FINE™/Turbo GUI The Rigid Motion model can be activated from the Optional Models / Fluid Structure page under the Mechanical tab. After activating the Mechanical Coupling, the Rigid Motion page will appear. It looks like Figure 7.3.2-7. FIGURE 7.3.2-7 The Rigid Motion page Firstly, the user needs to select the type of motion. Depending on this choice, all the parameters describing the motion law can be set by clicking on the button . FINE™/Turbo 7-13 Physical Models Fluid-Structure Three kinds of motion are available: • Oscillating Body: oscillation of a solid body about Z axis at a reference point. FIGURE 7.3.2-8 The parameters for Oscillating Body To define the motion, the user has to input the location of the rotation center (x,y) and the parameters describing the oscillations angle: The rotation axis is always Z for the oscillating body. α(0) A Frq Average angle; Amplitude of the oscillations; Frequency of the oscillations. Then the oscillating angle is computed by α ( t ) = α ( 0 ) + A sin ( 2π ⋅ Frq ⋅ t ) . • Off-centered Rotor: three kinds of basic motion for off-centered rotor can be simulated. These three basic motions can be combined to define more complex motions. FIGURE 7.3.2-9 The 7-14 parameters for Off-entered Rotor FINE™/Turbo Fluid-Structure Physical Models The rotation axis is always Z for the off-centered rotor. — Motion of the rotor center around Z axis (in XY plane). To describe the motion, the user has to input the following parameters: x(c), y(c) Location of the rotation center in XY plane; A Amplitude of the oscillations along X axis; B Amplitude of the oscillations along Y axis; α Angle at t = 0 in XY plane; ω Frequency of oscillations in XY plane; The location of the rotating axis of the rotor is obtained by: x RC ( t ) = x ( c ) + A cos ( α + 2πωt ⁄ 60 ) y RC ( t ) = y ( c ) + B sin ( α + 2πωt ⁄ 60 ) — Oscillation of the rotor center along Z axis. To describe the motion, the user has to input the following parameters: z(c) Location of the oscillation center in Z axis; C Amplitude of the oscillations along Z axis; β Angle at t = 0 along Z axis; ω Frequency of oscillations along Z axis. The location of the rotating axis of the rotor is obtained by: z RC ( t ) = z ( c ) + C cos ( β + 2πωt ⁄ 60 ) — Precession of the rotation axis around the absolute Z axis. Slanting the rotation axis allows more complex predefined motions. It is particularly interesting for precessions with a constant nutation angle. In this particular case, the rotation axis describes a cone. The Nutation Angle has to be inputed, which is defined in the plane OXZ at the initial time (t = 0). • Generalized Motion: the motion is specified by an external file. The user has to input the location of the rotation center (x,y,z) in the original mesh domain. FIGURE 7.3.2-10 The parameters for Generalized Motion In the external file, the motion has to be specified with 7 data for each time step: (Time, Δx,Δy,Δz,Δα,Δβ,Δγ) where Time: the simulated time; Δx: the displacement along X axis; Δy: the displacement along Y axis; Δz: the displacement along Z axis; Δα: the rotation angle around X axis; FINE™/Turbo 7-15 Physical Models Fluid-Structure Δβ: the rotation angle around Y axis; Δγ: the rotation angle around Z axis. All displacements and rotations must be specified in the absolute frame of reference. Consequently, the file must contain N+1 lines with N the number of time steps of the unsteady computation. The first line in the file is used to initialize the deformed mesh. For a restart computation, the previous time steps must be kept in the file and the total number of lines is Nprevious+N+1. The external file must be located in the computation directory with the name “projectname_computationname.evol_pos”. All solid patches and groups in the mesh are listed on the middle of the page, see Figure 7.3.2-7. After choosing the type of motion, the user has to select the moving surfaces and mark them as "Moving". c) Adaptive Wall The geometry simplifications imply sometimes that a moving wall is connected to a static wall. In reality, it is not possible and such simplifications must be avoided. For the computation, it is possible to consider an adaptive wall to fill the gap between moving and static walls, as shown in Figure 7.3.2-11. Adaptive wall is compatible only with the laplacian smoothing. The boundary vertices belonging to solid surface can move in order to have a better mesh quality. The displacement normal to the wall is zero for these vertices. FIGURE 7.3.2-11 Case with a simplified geometry where a moving wall is connected to a static wall The limitations on the adaptive wall are: • the adaptive wall must be located between a moving wall and a solid wall or a R-S interface; • the size of the adaptive wall must be large enough to take the imposed movements; • the subdivision of patches must keep the multigrid levels. To define an adaptive wall (fictitious wall), the user has to define the corresponding parts of wall in IGG™ as separated solid patches. These separated solid patches must be grouped and named as “Adaptative_wall” in the Boundary Conditions / SOLID page. 7-16 FINE™/Turbo Fluid-Structure Physical Models d) Expert Parameters The following expert parameters are related to the rigid motion module: IMVCRF(integer): The application of the mesh deformation is depending on the coordinate system. For example, for the off-centered motion, the displacement will be applied to the "Moving" walls specified by the user on the FINE™/Turbo GUI if the standard frame is used. Otherwise, the displacement will be used to the "stationary" walls if the relative frame attached to the solid body is used. The relative frame of reference can be defined by the expert parameter IMVCRF. 0(default): the standard rotating frame is used. 1: the relative frame attached to the solid body is used. 2: the relative frame is defined only by the translation of the body. This is used only for oscillating body in external flow. FIGURE 7.3.2-12 Moving surfaces depending on the value set to IMVCRF 7-3.2.2 MpCCI Coupling a) Introduction In addition to performing a thermal coupling simulation with MpCCI (see Chapter 7-3.1.2), the user can also perform a mechanical coupling, or both thermal and mechanical coupling simulation. When performing the mechanical coupling simulation with MpCCI, the FINE™/Turbo solver computes the flow around the structure and transfers the computed quantities to the structural solver. The displacements are therefore computed and transferred back to the FINE™/Turbo solver, which deforms the mesh. Then, the process is repeated until a steady state solution (steady mode) or the last physical time step (unsteady mode) is reached. For the mesh deformation, the user can select the Laplacian smoothing method or the Radial Basis Functions method (in Expert mode). For more information on the mesh deformation methods and its limitations, please refer to Chapter 7-3.2.4. The limitations on the mechanical coupling with MpCCI are as follows: • Wall forces exchange is not compatible with FNMB and condensable fluids. • Not compatible with coarse grid initialization and steady initialization. • No compatible with NLH. FINE™/Turbo 7-17 Physical Models Fluid-Structure Simulations coupling with MpCCI is available on the following platforms: AIX5.3 64bits, Linux 64bits and Windows 32/64bits. MpCCI v4 is supported b) Mechanical Coupling with MpCCI The mechanical coupling with MpCCI can be activated from the Optional Models / Fluid Structure page under the Mechanical tab. After selecting Mechanical Coupling and then Elastic Deformation, the mechanical coupling with MpCCI page will appear. It looks like Figure 7.3.2-13. All solid patches and groups in the mesh are listed on the middle of the page. The user has to select the coupled surfaces and mark them as "Coupled". FIGURE 7.3.2-13 The mechanical coupling with MpCCI c) Expert Parameters The expert parameters related to the mechanical coupling with MpCCI: ITCPL(integer): defines the number of iterations between each exchange with the coupled code for steady computation. 7-3.2.3 Modal Coupling a) Introduction FINE™/Turbo includes a modal coupling module in order to perform Fluid-Structure Interaction (FSI) simulations. For this kind of coupling simulation, a structure code is used to compute the modal shapes and the eigen frequencies of the structure. With these information the FINE™/Turbo flow solver will consider the interaction between the flow and structure and compute the deformation of the structure by solving the modal equations. 7-18 FINE™/Turbo Fluid-Structure Physical Models For the mesh deformation, the user can select the Laplacian smoothing method or the Radial Basis Functions method (in Expert mode). For more information on the mesh deformation methods and its limitations, please refer to Chapter 7-3.2.4. The limitations on modal coupling are as follows: • For unsteady computation, the time step should be less than one third of the period of the highest mode to avoid divergence. • Structure file containing mode shape definition must be written in SI units. • Modal coupling requires elastic mesh deformation. It involves all limitations linked to the mesh deformation methods. b) The Modal Coupling in the FINE™/Turbo GUI The modal coupling can be activated from the Optional Models / Fluid Structure page under the Mechanical tab, see Figure 7.3.2-14. FIGURE 7.3.2-14 The mechanical coupling with Modal The parameters related to modal coupling can be set by clicking on the button . The FINE™/ Turbo flow solver can model several structures. The user has to specify a Structure ID and Structure Name for each structure and set the corresponding parameters. Modal properties (eigen frequencies and modes shapes) are needed by the flow solver in order to compute the elastic deformation of the structures. These properties can be computed by a CSM code or measured experimentally. As modal resolution is a linear method, an initial deformation can be specified. This is useful to take into account non-linear effects independent of fluid load, such as centrifugal effect. A Structure File including these properties and the initial deformation (if any) must be imposed for each structure. The structure file must be written in ASCII format. First this file includes the number of dimensions of the structure, the number of modes, the number of structure nodes at which the modes are defined and a flag to specify if an initial deformation is specified. After that FINE™/Turbo 7-19 Physical Models Fluid-Structure the eigen frequencies are listed in increasing order. The frequencies have to be written in Hz. Finally the initial deformation and the mode shape information are written node by node. For each node one line contains the three (or two for 2D computation) coordinates, the initial deformation (if the parameter Initial deformation is set to 1) and the components of each mode sorted in increasing frequency order. Coordinates and mode shapes have to be written in SI unit system. For mode shape the conversion factor is the inverse of the square root of mass conversion factor. Mode shape must be scaled for a generalized mass equal to 1. FIGURE 7.3.2-15 The format of structure file Two kinds of method computing the displacement of the structure are available: Coupled and Forced Motion. In both methods, the user needs to specify the Number of Modes. The number of used modes must be less than or equal to the number of modes defined in the structure file. If the coupled method is selected, a Damping Coefficient needs to be specified for each mode used. These damping coefficients will be used to solve the modal equations and compute the deformation of the structures. If the forced motion is selected, the Generalized Displacement needs to be specified for each mode used. The generalized displacement can be a constant value (steady or unsteady mode) or a time profile (unsteady mode). These generalized displacements will be used to compute the deformation of the structures directly. For more information on how to compute the deformation of the structures, please refer to the theoretical manual. After setting the modal parameters, the user has to specify the boundaries corresponding to the structure surfaces. All solid patches and groups in the fluid mesh are listed on the middle of the page. The user has to select the coupled surfaces, mark them as Coupled and specify the corresponding Structure ID. With the modal approach, a new output file is generated with the extension ".generalized_motion". This file has the following format: • for steady computation: the iteration number, q for each mode and each structure defined in the interface, where q is the generalized displacement. 7-20 FINE™/Turbo Fluid-Structure Physical Models 2 q ------ , d-------• for unsteady computation: the time step, q , dq for each mode and each structure defined 2 dt dt in the interface, where q is the generalized displacement. 7-3.2.4 Mesh deformation methods Mesh deformation plays a crucial role in the analysis of multi-physics problems that involve moving bodies and domain with dynamic boundaries. For example, in Fluid-Structure Interaction (FSI), the fluid mesh has to be deformed at each time step according to the displacements computed by the structural solver at the interface of the fluid domain and solid domain. In FINE™/Turbo, two kinds of mesh deformation methods are available: Laplacian smoothing and Radial Basis Functions. The user can select them in expert mode when Mechanical coupling is activated, see Figure 7.3.2-7. For all computations with mesh deformation, a ".globalforce_unsteady" file is generated, which contains the evolution of the load on solid surfaces. The ".globalforce_unsteady" file has the following format: • for steady computation: • for unsteady computation: The first set of is for the surfaces for which the option Compute force and torque has been activated in the Boundary Conditions page under SOLID tab. The second one is for the other solid surfaces. a) Laplacian Smoothing The Laplacian smoothing method assumes that the mesh deformation caused by a moving solid wall boundary is small enough so that the mesh topology is not modified and the mesh can be smoothed without generating negative cells. This assumption of small displacements on the moving solid boundary allows to keep the same mesh topology and generate the new mesh with a Laplacian smoothing of these displacements inside the domain. The smoothing of displacements is carried out only to groups where a surface is moving. The main limitations for the groups of blocks where the mesh is deformed are as follows: • no FNMB connection; • no SNG boundary conditions; • no rotor-stator interface with deformation; • rotor-stator interface can not be located between moving walls; b) Radial Basis Functions The Laplacian smoothing works only when the mesh deformation is very small. When performing a MpCCI or modal mechanical coupling simulation, the structure deformation may be very large. In this case, the mesh deformation method using Radial Basis Function (RBF) can be used. The RBF method gives deformed meshes keeping very good quality even for large deformation. For more information on the RBF method, please refer to the theoretical manual. The main limitations for the RBF mesh deformation method are as follows: FINE™/Turbo 7-21 Physical Models Fluid-Structure • The mesh deformation method using RBF is not compatible with: — FNMB connections, — SNG boundary condition, — Upwind scheme, — Rigid body motion, — Adaptive wall. • The number of boundary nodes is limited to 46000 per blade row. Please note that memory cost can become quite huge when the number of boundary nodes increases. c) Expert Parameters IMOVWD(integer):When mesh deformation exists, the wall distance used for turbulent flow may change. In this case, the user can set the expert parameter IMOVWD to 1 to compute the wall distance at each time step. 0(default): compute the wall distance only once. 1: compute the wall distance at each time step. The expert parameters related to Laplacian smoothing: IMVCYL(integer): The smoothing can be applied to the displacement field in cartesian coordinates or in cylindrical coordinates. The best choice is depending on the geometry of the case. 0(default): applied in cartesian coordinate. 1: applied in cylindrical coordinate. FCTNIT (real): Multiplicative factor for the number of smoothing iteration. The number of iteration (N) for the full multigrid initialization on grid level G is based on the maximum number of points in each direction in all blocks: N (on grid level G) = FCTNIT*(G+1)*MAX(NI, NJ, NK) If the deformed mesh has negative volumes, the user can increase this expert parameter. MVRELF (real): Relaxation factor of the iterative process (default = 0.9). A mesh with high aspect ratio and skewed cells requires lower value (0.45). If the iterative process of the mesh deformation is unstable, MVRELF must be decreased (<0.5). IMVWEI (integer):Select the smoothing method for the moving mesh: 0 (default): Linear smoothing of displacements; 1: Weighted smoothing of displacements based on the cell volume in the nodeformed mesh. The weighted smoothing allows to restrict the smoothing of the small volume cells in order to preserve the quality of the mesh. The smaller cells are more rigid than bigger cells. MVDIFF (real): Relaxation factor for the weighted elliptical smoothing of displacements. The expert parameters related to mesh deformation module (RBF): MOVRBF(integer):Choice of RBF function. 1: Wendland C2 function, 7-22 FINE™/Turbo Passive Tracers Physical Models 2(default): TPS function. MOVRAD(real): Support radius for Wendland C2 function or scale factor for TPS function. ISVMAT(integer): Choice of the solving method for system of equations. 0: don’t use inverse matrix, 1(default): compute, save and use inverse matrix, 2: use inverse matrix that has already been computed and saved. ICOARS(integer): Controls the coarsening level of the boundaries. It only affects the mesh deformation step. This parameter is an array of two dimensions, corresponding to coarsening level for moving boundaries and fixed boundaries. The first number is the grid level (relative to the grid level of the computation) of moving boundary nodes used for the deformation. The second number is the grid level for the fixed boundary (solid, inlet, outlet, periodic,...) nodes. If the grid level is set to 0, all the nodes of the surface are taken into account. If it is set to one, only the nodes of the surface belonging to the first coarser grid are used. Hence the number of boundary nodes is reduced by four for the surface. 7-4 Passive Tracers Selecting the Passive Tracer option in the Configuration / Flow Model page allows the user to introduce, into the computations, species that are passive with regards to the carrier fluid. This means that the carrier fluid ignores the tracer and is only defined by its own properties. • The passive tracers are not allowed to react with each other. 7-4.1 Boundary Conditions There are currently two types of boundary conditions available in the FINE™/Turbo solver for passive tracers: inlet and external (far field). The inlet condition is set through the specification of the species mass fractions ρ s ⁄ ρ where ns ρ= ρs with ns, the total number of species. The external condition requires the same input data. s=1 For passive tracers, species concentrations are entered and are independent from each other. There is no limitation on the sum of the concentrations. 7-4.2 Initial Solution For each species, the initial value of the mass fraction at the initial stage is required. Initial conditions are uniform over the domain for each species. FINE™/Turbo 7-23 Physical Models Porous Media Model For passive tracers, species concentrations are entered and are independent from each other. There is no limitation on the sum of the concentrations 7-4.3 Outputs For each species, the FINE™/Turbo solver will compute automatically the species concentration for each tracer. 7-5 Porous Media Model A porous medium is a solid permeated by an interconnected network of pores filled with a fluid. Usually both the solid matrix and the pore network are assumed to be continuous, so as to form two interpenetrating continua such as in a sponge. Many natural substances such as rocks and soils, and man made materials such as foams and ceramics can be considered as porous media. When simulating the flow in porous media the user has to use a porous media model because the geometry is too complex to resolve with a grid. The porous media model in FINE™/Turbo allows the user to simulate the flow in porous media. In FINE™/Turbo, the user needs to set which grid block will be treated as a porous medium. And the user has to specify the parameters for each block. In the next sections the following information is given on the Porous Media Model: • 7-5.2 gives a summary of the available expert parameters related to the Porous Media Model. 7-5.1 Porous Media Model in the FINE™/Turbo GUI There is no access of Porous Media Model through the graphical user interface. The user has to activate this model and set all the parameters through the Expert Parameters, as describing in the following part. 7-5.2 Experts Parameters IPORME (integer):Control if activate the porous media module or not: 0: module is deactivated (default) 1: module is activated IDOMPO (integer):Porous media domain number (no more than 50 domains). IDIRPO (real): Imposed direction for each specified porous block (if 0 0 0, no direction is imposed). IMODPO (integer):Select the models available to model the pressure drop through the porous media: 1: Darcy or Ergun law 2: Integral law LPORME (real): Porous medium thickness (L), used only if IMODPO = 2. 7-24 FINE™/Turbo Cavitation Model Physical Models EPORME (real): Porosity ( ε ), used only if IMODPO = 1, is defined as the volume fraction of the voids from the solid matrix KPORME (real): Constant C in the models. APORME (real): the specific surface area A in the Ergun or Darcy model and A total ⁄ A passage in the integral model. NPORME (real): Exponent n, used only if IMODPO = 2. ITHEPO (integer): Control if activate the thermal source term in the porous media or not: 0 (default): Activate the thermal source term 1: Deactivate the thermal source term HPORME (real): Heat transfer coefficient for porous media. SPORME (real): Volumetric exchange surface. TPORME (real): Skin temperature. 7-6 Cavitation Model Cavitation is a dynamic process of formation of bubbles inside the liquid, their growth and subsequent collapse. It appears where the pressure of the liquid falls below its vapor pressure. Such cavitation often occurs in pumps, nozzles, injectors and marine etc. Cavitation is an abnormal condition that can result in loss of efficiency, increase of the noise level and structural damage. The development of the cavitation phenomena is related to the cavitation number σ . Cavitation develops with decreasing the cavitation number. More details can be referred to the theoretical manual. In the next sections the following information is given on the Cavitation Model: • 7-6.2 gives a summary of the available expert parameters related to the Cavitation model. 7-6.1 Cavitation Model in the FINE™/Turbo GUI There is no access of Cavitation Model through the graphical user interface. The user has to activate this model and set all the parameters through Expert Parameters, as describing in the following part. 7-6.2 Experts Parameters IMITRA (integer): control the activation of the cavitation model 0: model is inactive (default) 2: model is active Parameters related to the definition of the fluid: PVAPS (real): vapor pressure [Pa] (default = 2000, cold water) RHOL (real): density in liquid phase [kg/m3] (default = 1000, cold water). FINE™/Turbo 7-25 Physical Models Cavitation Model RHOV (real): density in vapor phase [kg/m3] (default = 1, cold water). AMIN (real): related to the maximum slope of the barotropic law (default = 50, cold water). A min = ρL – ρV 2 ----------------- c min 2 where cmin is the celerity of sound in the homogeneous liquid-vapor mixture. Parameters related to the numerical scheme: VIS2SW (integer): 1: second order pressure switch is de-active (default) 0: second order pressure switch is active (suggested for incompressible flows) RSMPAR (real): 1: residual smoothing is active (default) 0: residual smoothing is de-active (suggested for incompressible flows) VAPLAX (real): 7-26 under relaxation coefficient for pressure. This parameter will be activated when ρ = ρV and/or static pressure drops during run. FINE™/Turbo CHAPTER 8: 8-1 Dedicated Turbomachinery Models Overview The following models and modules in FINE™/Turbo are dedicated to turbomachinery applications: • Rotating Blocks defines the typical information concerning cylindrical cases for each block. • Rotor/Stator Interaction defines the properties of each rotor/stator interface. • Harmonic Method allows to perform unsteady simulation using Harmonic method. • Clocking allows to consider the effect of clocking in multistage turbomachinery case. • Cooling/Bleed models cooling holes or bleed. • Rigid Motion models the flow where the solid walls can move. • Aeroacoustics models acoustic noise based on harmonic computation. • Laminar-Transition Model models the flow transition. • Performance Curve allows to perform an off-designed analysis for turbomachinery. • SubProject Management allows the partial treatment of multistage turbomachinery projects 8-2 Rotating Blocks The Rotating Blocks tab gives access to the definition of the typical information for each block as shown in Figure 8.2.0-1. This tab is only accessible when the mesh is cylindrical (see Mesh/Properties... to see whether the mesh is cylindrical or Cartesian). FINE™/Turbo 8-1 Dedicated Turbomachinery Models FIGURE 8.2.0-1 Rotating Rotating Blocks Blocks on Rotating Machinery Page When selecting the Rotating Blocks tab the page appears as shown in Figure 8.2.0-1. On the left a list of all blocks is displayed. If the mesh has been made with AutoGrid™, a default grouping per row is proposed. It is also possible to manually group the blocks that have the same properties: 1. Clicking on a block de-selects the currently selected block(s). It is possible to select several consecutive blocks in the list by clicking on the first one and holding the left mouse button while selecting the next. To select a group of blocks which are not situated next to each other, click on each of them while keeping the key pressed. 2. Click on the Group button. A text box will appear just below the Group button. Place the cursor in the text box and type the name of the group and press . The name of the group will appear on the list of blocks in red with a plus sign on the left of the name. To see the blocks that are included in a certain group double click on the name of the group or click on the symbol in front of the name. 3. To remove a group of blocks select the group and click on the Ungroup button. The group will be removed and the blocks that were in this group will be listed again in the list as separate blocks. 4. The Reset Turbo Groups button allows to reset the default grouping proposed by AutoGrid™. On the right of the list with blocks, the information for the selected block or group of blocks is given. If multiple blocks are selected the information is only displayed for the first selected block. For each block the current and maximum number of nodes in the three grid directions is shown. Four items need to be defined by the user: the streamwise direction, the spanwise direction, the azimuthal direction and the rotational speed: — The streamwise, spanwise and azimuthal directions allow to determine the block orientation. Please note that if AutoGrid™ is used for the grid generation, the streamwise direction is automatically taken as being the k-direction, the spanwise direction as the j-direction and the azimuthal direction as the i-direction. The block orientation has an impact when using the radial equilibrium outlet (spanwise direction used), when performing an azimuthal or surface averaging (respectively spanwise and streamwise direction used). 8-2 FINE™/Turbo Rotating Blocks Dedicated Turbomachinery Models — The FINE™/Turbo solver solves the equations in a relative frame of reference. This implies that the mesh blocks surrounding rotating blades rotate with the blades and should therefore be set as "rotating" in this page. The Rotational Speed of the block has to be given in Revolutions Per Minute (RPM). A positive value for the rotation speed indicates a rotation in positive θ-direction with θ positive according to a right handed coordinate system. In Figure 8.2.0-2 this is illustrated for the case where the z-axis is the axis of rotation which is automatically the case for a mesh created with AutoGrid™. FIGURE 8.2.0-2 Positive rotation speed Although the governing equations for rotating systems are usually formulated in the relative system and solved for the relative velocity components, the formulation retained for ship propeller applications, ventilators or wind turbine are often expressed in the relative frame of reference for the absolute velocity components. The two formulations should lead to the same flow solution. However, experience shows that the solution can be different, especially in the far field region. For propeller problems, the formulation based on relative velocities has the disadvantage that the far field relative velocity can reach high values. This induces an excess of artificial dissipation leading to a non-physical rotational flow in the far field region, this dissipation being based on the computed variables. In FINE™/Turbo, the governing equations for rotating systems can be solved for the relative velocity components or for the absolute velocity components, which is controled by setting the expert parameter IVELSY to 1 or 0. The different computations in a project can not have different configuration settings. If any of the settings in this area are changed, the modifications will be taken into account for all (active and non-active) computations. The rotation axis should be the z-axis in order to be compatible with the FINE™/ Turbo solver. Only one rotation speed different than 0 is allowed when performing an unsteady simulation using the Domain Scaling method or Phase lagged method. FINE™/Turbo 8-3 Dedicated Turbomachinery Models Rotor/Stator Interaction 8-3 Rotor/Stator Interaction 8-3.1 Rotor/Stator Interfaces in the FINE™/Turbo GUI The Rotor-Stator tab gives access to the definition of the rotor/stator interfaces as shown in Figure 8.3.1-3. This tab is only accessible when the mesh contains rotor/stator interfaces. Rotor/stator interfaces are defined in IGG™ as ROT boundary condition. Consult the IGG™ User Manual for more detailed information on how to define this boundary condition. The rotor/stator patches should not include regions where R=0. On the left, the list of patches is displayed which are defined as part of a rotor/stator interface in IGG™ (boundary condition type: ROT). It is possible to display only a limited amount of patches by using the Filter. Type in the text box the part of the name that is common to all patches to display and press . All patches containing in the name the entered text will be displayed. Note that the filter is case insensitive. If the mesh has been made with AutoGrid™, a default grouping is proposed. It is possible to group patches that have the same definition by selecting them in the list and clicking on the Group button. A text box will appear below this button which allows to enter a name for the group. The group will be displayed in red in the list of patches. Double click on the group name to see which patches are in the group. To select multiple patches select them while keeping the key pressed. To remove the group simply select the group from the list and click on Ungroup. The patches in the selected group will be put back into the list of patches and the group name will be removed from the list. In some special cases where the mesh is made by AutoGrid5™ (e.g. bypass configuration), the upstream and/or downstream patches can not be grouped automatically. In this case, the user has to pay attention to the rotor/stator interface definition to see if the mesh constraints are ensured. Multiple rotor/stator interfaces can be treated in one single project. Each rotor/stator interface is indicated by an ID Number and each of them may contain an arbitrary number of Upstream and Downstream patches. For each patch in the list, the ID number of the corresponding rotor/stator interface has to be provided by the user. Also it should be specified whether the patch is located in the upstream or downstream side of the interface. It should be mentioned that no hypothesis is made on the direction of the flow through the interface, except when the transition module (see section 89) or the stage-by-stage analysis (see section 10-3.2) is used. The purpose of the upstream and downstream denominations is only to establish the two groups of patches belonging to respectively the rotor and the stator side. 8-4 FINE™/Turbo Rotor/Stator Interaction Dedicated Turbomachinery Models FIGURE 8.3.1-3 Rotor-Stator interface definition in steady mode In addition to the ID number and the upstream/downstream side specifications the user has to select also: • the order of Extrapolation (zero or first order). Zero order extrapolation (default) is used in most cases and usually provides satisfactory results. First order extrapolation may be useful in case of important flow gradients in the direction normal to the interface together with a relatively coarse mesh. • one of the six available steady state techniques (for steady state applications only): The type of several rotor-stator interfaces can be changed simultaneously by selecting one rotor-stator interface, hold the button and left-click on the desired type of rotor-stator interface. All other settings, such as the ID Number, will be kept. — 1. The Conservative Coupling by Pitchwise Rows approach is recommended due to its capability to provide an exact conservation of mass flow, momentum and energy through the interface. This approach adopts the same coupling procedure for all the nodes along the circumferential direction, even if the local flow direction is different from the averaged one. This technique offers the advantage of being able to guarantee a strict conservation of mass, momentum and energy through the interface. Moreover it shows to be very robust and is therefore used by default. — 2. The Local Conservative Coupling approach is only recommended for the rotor/stator interface between an impeller and a volute. Experience has shown that in cases, where significant flow variations are observed in the circumferential direction (as for instance in the case of rotor-volute interactions), it is more stable to base the flux decomposition on the local flow direction as it is done in the Local Conservative Coupling technique. Small conservation errors can be observed with this technique, which is therefore only used for special configurations. — 3. The Full Non Matching Mixing plane approach is respecting an exact conservation of mass flow, momentum and energy through the interface as the Conservative Coupling by Pitchwise Rows but has less constraints on the interface geometry. FINE™/Turbo 8-5 Dedicated Turbomachinery Models Rotor/Stator Interaction — 4. The Full Non Matching Frozen Rotor approach is considering the rotor/stator interface as a perfect connection and is neglecting the rotor movement in the connecting algorithm. In this approach, the periodicities between rotor stator must be equal. — 5. The Non Reflecting 1D approach is based upon a characteristic analysis of the linearized Euler equations. The characteristic variables are imposed on each side of the rotor/stator interface. Such a treatment is recommended when wave reflection is observed at the interface, which can occur when the interface is close to the blade. — 6. The Non Reflecting 2D approach is the extension of the Non Reflecting 1D approach. The Non Reflecting 2D approach is also based upon a characteristic analysis of the linearized Euler equations. The characteristic variables are imposed on each side of the rotor/stator interface. The Non Reflecting 2D approach will produce a better representation of the shock wave crossing a R/S interface. The Non Reflecting 1D/2D approach can not be used when the flow perpendicular to the rotor/stator interface is supersonic. The use of the Non Reflecting 1D/2D approach is limited to steady simulations without preconditioning. The Non Reflecting 1D/2D approach is only compatible with perfect gas or real gas. 8-3.2 How to Set-up a Simulation with Rotor/Stator Interfaces? Five different approaches are available in FINE™/Turbo to simulate the interaction between rotating and non-rotating blocks: Steady state: • Mixing plane approach: a pitchwise averaging of the flow solution is performed at the rotor/ stator interface and the exchange of information at the interface depends on the local direction of the flow. See section 8-3.2.1 for more detail on how to use this approach. • Frozen rotor: a steady simulation of one specific position of the rotor with respect to the stator. For more information on how to set up a project according to this method see section 83.2.2. Unsteady: • Domain scaling method: unsteady simulation in which the mesh periodicities are constrained to be identical on both sides of the interface. See section 8-3.2.3 for more detail on how to use this approach. • Phase lagged method: unsteady simulation in which the mesh periodicities are not constrained to be identical on both sides of the interface. See section 8-3.2.4 for more detail on how to use this approach. • Harmonic method: like the phase-lagged method, this method only needs one inter-blade channel per blade row. No special requirement on the periodicities is required. The interaction between two adjacent blade rows is modelled by computing the time harmonics of the fluctuating part of the unsteady flow along the two sides of the rotor/stator interface as well as the time-averaged flow. The values are calculated with respect to the matching of the unsteady flow on both sides of the interface and are treated locally by a non-reflective treatment. A mixing-plane approach is applied to the eddy-viscosity if the Spalart-Allmaras model is used. See section 8-3.2.5 for more detail on how to use this approach. 8-6 FINE™/Turbo Rotor/Stator Interaction Dedicated Turbomachinery Models 8-3.2.1 Mixing Plane Approach In the mixing plane approach the flow solution at the rotor/stator interface is azimuthally averaged and the exchange of information at the interface depends on the local direction of the flow. In this section it is described how to use this approach in FINE™/Turbo. a) Geometrical Constraints The default mixing plane method (Local Conservative Coupling and Conservative Coupling by Pitchwise Rows) used in FINE™/Turbo imposes the following geometrical constraints: • The patches on both sides of the rotor/stator interface must cover the same range in spanwise direction, • The meshes need not to match in the spanwise direction, but the azimuthal mesh lines on the boundary must be circular arcs. An illustration of these constraints is given in Figure 8.3.2-4. Consisting of two stripes, the depicted configuration provides a complete description of the capabilities. The upstream side of the quasisteady interface consists of three blocks, represented by the bold frames and the surface meshes, while a single block is assumed for the downstream side. A gap may exist between two blocks, e.g., if the mixing plane coincides with the exit plane of a blade row having a blunt trailing edge. The grid points distribution are different for each of the boundary patches involved, but the pitchwise grid lines have constant radius and the pitchwise line along which two patches of the same side join (e.g., BC 1 and BC 3) exists as an inner grid line on all other boundaries. In the example, the interface is thus decomposed into two stripes, stripe 1, consisting of BC 1 and BC 2 on the upstream side and BC 5 on the downstream side, and stripe 2, consisting of BC 3 and BC 4 on the upstream side and BC 6 on the downstream side. In special configurations such as rotor-volute interaction it is preferable to use Local Conservative Coupling. . FIGURE 8.3.2-4 Example FINE™/Turbo of stripe configuration 8-7 Dedicated Turbomachinery Models Rotor/Stator Interaction The full non matching mixing plane method (Full Non Matching Mixing plane, Non Reflecting 1D and Non Reflecting 2D) removes the geometrical constraints imposed in the default mixing plane method. This technique is based on the full non-matching algorithm and has clear advantages: an exact conservation of the mass flow, momentum and energy is guaranteed. The remaining geometrical constraints for the full non matching mixing plane method are: • The rotor/stator patches belonging to a given interface should lie on the same common axisymmetric surface. • The hub and the shroud lines are assumed to be located on a circular arc, and each extremity of the hub and shroud lines should coincide with one corner of one of the patches. The periodic boundaries between the adjacient blades must be defined by continuous lines with edges connected by their corners. For a 360-degree mesh, a similar continuous spanwise line (defined by interconnected edges) must be used in the connection algorithm. • All patches constituting a rotor/stator interface should form a filled closed surface with no gap. • the rotor/stator patches should be fully included in the rotor/stator interface: contrary to the full non matching algorithm, which includes an automatic detection of the connection zone, and in which the patches can then be partially connected, the rotor/stator module assumes that the patches are fully connected. b) Mesh Constraints Only one blade passage needs to be meshed for both the rotor and the stator, regardless of their respective periodicities. The boundary condition type must be set to "ROT" in IGG™ for all grid patches belonging to a rotor/stator interface. c) FINE™/Turbo Settings 1. The mixing plane approach is a steady simulation technique which requires to set the Time Configuration to Steady on the Flow Model page. 2. The patches that have boundary condition type "ROT" in the mesh are listed in FINE™/Turbo on the Rotating Machinery page under the Rotor-Stator tab. The user has to specify for each of these patches: • an ID Number that identifies the rotor/stator interface (useful for multistage configurations). • a switch to indicate if the patch is belonging to the Upstream or Downstream part of the rotor/stator interface. • the order of Extrapolation (zero or first order). • the boundary condition: — Conservative Coupling by Pitchwise Rows, — Local Conservative Coupling, — Full Non Matching Mixing plane, — Non Reflecting 1D. — Non Reflecting 2D. 8-8 FINE™/Turbo Rotor/Stator Interaction Dedicated Turbomachinery Models ID = 2 Upstream Upstream Downstream Downstream ID = 1 Flow Direction FIGURE 8.3.2-5 Aachen Turbine: Upstream/Downstream and ID number identification d) Illustrative Example To illustrate the mixing plane approach the flow around a cube is considered as shown in Figure 8.3.2-6. The flow is entering the domain at the bottom of the figure. The upstream portion of the domain is the 'rotor' with a cube fixed on it. The second part is a 'stator'. Due to the pitchwise averaging process one can see that the vortex occurring slightly downstream the 'trailing edge' of the cube is spread when entering in the 'stator' component. If the rotational speed of the cube is high, this approximation is acceptable since one can consider that the stator "sees" a more statistically averaged flow. If the rotational speed is low, this approximation is essentially invalid and thus another method should be considered. In some cases, i.e. in low pressure ratio compressors or turbines, the losses at the rotor/stator interfaces are in the order of magnitude of the overall gain in the machine. In such cases, it is recommended to use an unsteady approach and more specifically the harmonic approach (section 8-3.2.5) FIGURE 8.3.2-6 Flow FINE™/Turbo around a cube: Mixing Plane approach 8-9 Dedicated Turbomachinery Models Rotor/Stator Interaction e) Expert Parameters This section provides a summary of the expert parameters related to mixing plane approach. CFFNMB(integer):0 (default): old implementation for FNMB connection 1: new implementation with connection factor of cell area between image mesh and actual mesh. NQSTDY(integer): gives the possibility to the user to update the rotor-stator boundary conditions every NQSTDY iterations. If the parameter NQSTDY is set to zero (default), the update is done at every Runge-Kutta step. This is an under-relaxation technique that is rarely used. Before the mixing process, an under-relaxation technique can be applied on the averaged variables to stabilize the calculation: RQSTDY(real): This is another under-relaxation technique that allows to limit the changes in the variables from one iteration to the next. This technique is used in special cases where stability problems are encountered. 1 (default): no relaxation 0 to 1: under-relaxation IRSMRG(integer): This parameter is used only for the Conservative Coupling by Pitchwise Rows method and the Local Conservative Coupling method in parallel simulations. It is linked to memory allocation for merging of spanwise distribution. The allocation will be based on the value of IRSMRG multiples the maximum number of points in different distributions. RSROL(real): This parameter is the tolerance used for the Full Non Matching Plane algorithm (default value 1.8). This parameter should be smaller than the ratio of the first inner cell distance to the hub-to-shroud distance. NH2DNR(integer): sets the number of harmonics used for DFT and inverse DFT when using the non-reflecting 2D Rotor/Stator interface. The default value is 3. LOCCOR(integer) In some particular cases, a problem of mass flow conservation through a non reflecting 1D or 2D rotor-stator interface can arise. This can be improved by deactivating the local enthalpy correction through the expert parameter LOCCOR. 0: local enthalpy correction deactivated 1 (default): local enthalpy correction activated 8-3.2.2 Frozen Rotor The basic idea at the origin of the frozen rotor technique consists of neglecting the rotor movement in the connecting algorithm. The governing equations are solved for the rotor in a rotating frame of reference, including Coriolis and centrifugal forces; whereas, the equations for the stator are solved in a absolute reference frame. The two components are literally connected, and hence a rotor-stator approximation is not required, rather the continuity of velocity components and pressure is imposed. As a result, the final steady solution will be depending on the relative position of the rotor and the stator. Unsteady 'history effect' (such as shedding separated zones) are neglected. It is usually well accepted that the frozen rotor approach is an appropriate solution for the treatment of rotor-volute interactions, where pitchwise variations of the flow cannot be neglected. However, it 8-10 FINE™/Turbo Rotor/Stator Interaction Dedicated Turbomachinery Models requires the meshing of the complete impeller (all passages). Another drawback is that the flow solution depends on the rotor position, relative to the stator. a) Mesh Constraints Exactly as for the domain scaling approach a constraint must be satisfied on the mesh periodicity. The pitchwise distance must be the same for both sides of the rotor/stator and coincident (no gap allowed between rotor and stator components in the pitchwise direction). For each different position of the rotor with respect to the stator a new mesh will have to be created in IGG™ and a new steady calculation has to be performed. b) FINE™/Turbo Settings There are three ways to run a frozen rotor calculation: 1. To mesh all blade rows completely and to use matching connections (CON) in IGG™ for the patches at the interface of the rotor and the stator. The blocks of the rotor should be made rotating, as well as the boundary conditions. A steady calculation can be run for this configuration. A non matching (NMB) connection can not be used in this case: even though the computation might run the result would not be correct. This was previously the only way to perform frozen rotor calculations in FINE™/Turbo. This approach is no longer used as the constraint on matching connections is too restrictive. Only CON matching connections are allowed in this first method. 2. To create a mesh covering the same pitchwise distance on both sides of the interface and to impose Full Non Matching Frozen Rotor in the Rotating Machinery page under the RotorStator tab. Furthermore the user has to specify for each of these patches the ID and the upstream/downstream location as described in section c) at step 2. Therefore, the boundary condition type must be set to "ROT" in IGG™ for all grid patches belonging to a rotor/stator interface. 3. When starting an unsteady computation by imposing iterations as a steady initialization in the Control Variables page, the frozen rotor technique is used during the steady iterations. Note that for example for an impeller-volute computation the complete impeller would need to be meshed in all three cases since the periodicity of the volute is 1. c) Illustrative Example Results obtained from frozen rotor calculations usually look similar to unsteady ones. A more detailed analysis shows that the approximation introduced in the connection algorithm induces a deviation of the wake when passing through the interface. As an illustration the frozen rotor method is compared to the sliding mesh approach for the Aachen Turbine in Figure 8.3.2-7 and Figure 8.3.2-8. FINE™/Turbo 8-11 Dedicated Turbomachinery Models Rotor/Stator Interaction FIGURE 8.3.2-7 Aachen Turbine: Frozen Rotor approach 8-3.2.3 Domain Scaling Method The Domain Scaling Method is an unsteady simulation technique for rotor/stator interfaces. The effect of displacement due to rotation is taken into account. At each time step, the rotor is set at its correct position and equations are solved for that particular time step for the whole computation domain. The final solution is therefore a succession of instantaneous solutions for each increment of the rotor position. FIGURE 8.3.2-8 Aachen 8-12 Turbine: Domain Scaling (Sliding Mesh) approach FINE™/Turbo Rotor/Stator Interaction Dedicated Turbomachinery Models a) Mesh Constraints The boundary condition type must be set to "ROT" in IGG™ for all grid patches belonging to a rotor/stator interface. The blade passages of each blade row to include in the mesh should cover the same pitch distance (have the same periodicity). If the periodicity of the rotor and the stator is not the same this can be solved in three different ways: • modelling a higher number of blade passages on each side to find a common periodicity, • scaling the geometry (with the scaling being as close to 1 as possible). The common way to scale the geometry is to modify the number of blades during the mesh generation process. The time frequencies are resolved with an error that is proportional to the scaling coefficient. • using the phase lagged approach explained in section 8-3.2.4 or the nonlinear harmonic method in section 8-3.2.5. Apart from this constraint on the periodicity, there is no constraint on the patches and mesh nodes configurations. b) FINE™/Turbo Settings 1. Domain Scaling Method is an unsteady simulation technique so the Time Configuration in the Flow Model page should be set to Unsteady. 2. By default, in the Rotating Machinery page under Rotor-Stator tab page, the Domain Scaling approach is selected. The user has to specify for each of these patches the ID and the upstream/ downstream location as described in section c) at step 2. Therefore, the boundary condition type must be set to "ROT" in IGG™ for all grid patches belonging to a rotor/stator interface. 3. The initialization process can be performed in two ways: • A steady state initialization is performed in a separate computation with Steady as Time Configuration. It is suggested to model all rotor/stator interfaces in this case using frozen rotor approach. The unsteady domain scaling computation is using the result of this steady computation as initial solution. See Chapter 9 for more information on how to start a computation from an initial solution file. • The steady state initialization is automatically performed before starting the time accurate computation (that means within the same computation), switching to Unsteady as Time Configuration in the Flow Model page and selecting in the interface an appropriate Number of Steady Iterations in the Steady Initialization parameters on the Control Variables page. 4. The Number Of Angular Positions is defined in the Control Variables page. When working with the Domain Scaling method, using a Number Of Angular Positions of 10 points per blade passage is giving a coarse but reasonable result. To have a more accurate (but more CPU consuming) result choose 20 to 30 points per blade passage. 5. The Number Of Time Steps is defined in the Control Variables page. In general, it is recommended to repeat the period at least 20 times. Usually after 20 periods, the flow becomes periodic. For example, considering a 1-1/2 turbine with the blade number of 43, 64 and 16. The user can generate a scaled multi-row mesh including 8 stator passages, 12 rotor passages and 3 stator passages with a common periodicity of 5. In this case the user needs at least 10 time steps for each rotor passage and that is really a coarse result. So the minimum Number of Angular Positions is 120. Usually, 20 periods are needed to reach periodic flow. The user will have to set the Number Of Time Steps to 2400. 6. For more info on the Outputs Files available in the Control Variables page, see section 6-3.1. FINE™/Turbo 8-13 Dedicated Turbomachinery Models Rotor/Stator Interaction c) Illustrative Example For the example case of the flow around a cube where the flow is entering the domain at the bottom of Figure 8.3.2-9. The upstream portion of the domain is the 'rotor' with a cube fixed on it. The second part is a 'stator'. With the domain scaling approach, one can observe a strong vortex shed into the stator passage, leading to a correct physical simulation of the unsteady phenomenon (at the expense of much higher CPU time compared to mixing plane approach). FIGURE 8.3.2-9 Flow around a cube: Domain Scaling method d) Expert Parameters The following expert parameters can be used with an unsteady computation using domain scaling method: Parameter for Saving/Reading of FNMB data of rotor-stator interface: IFRSFI(integer) 0: FNMB data computed but not saved 1: FNMB data computed and results saved in .adf file. 2 (default): FNMB data computed and results saved if the .adf file is not existing. Results read from .adf file otherwise. ICYOUT(integer): 1 is used in combination with Multiple Files option to avoid overwriting of the output files at each blade passage. 8-3.2.4 Phase Lagged Method The Phase Lagged Method is an unsteady simulation technique for rotor/stator interfaces. The effect of displacement due to rotation is taken into account. At each time step, the rotor is set at its correct position and equations are solved for that particular time step for the whole computation domain. The final solution is therefore a succession of instantaneous solutions for each increment of the rotor position. This method is allowing the user to reduce the CPU time needed for computing an unsteady simulation of a turbomachinery stage (rotor-stator interaction). This capability has been implemented as an additional functionality into the release FINE™/Turbo. 8-14 FINE™/Turbo Rotor/Stator Interaction Dedicated Turbomachinery Models If a phase lagged computation should be used as an initial solution for another computation, the .res and the .bpl files must be manually copied to the new computation directory. The phase lagged method is only allowed for one stage computations (stator-rotor). For multi-stage computations, such as a 1-1/2 stage computation (stator-rotor-stator), it is only possible if the number of both stators is the same. a) Mesh Constraints The only constraints is that the boundary condition type must be set to "ROT" in IGG™ for all grid patches belonging to a rotor/stator interface. It is recommended to have an overlapping region in the circumferential direction between the channel(s) of the rotor and the channel(s) of the stator. b) FINE™/Turbo Settings 1. The Phase Lagged Method is an unsteady simulation technique so the Time Configuration in the Flow Model page should be set to Unsteady. 2. At the top of the Rotating Machinery page, the Phase Lagged option has to be activated and under Rotor-Stator tab, the Phase Lagged approach is selected automatically. However the user has to specify for each of these patches the ID and the upstream/downstream location as described in section c) at step 2. Therefore, the boundary condition type must be set to "ROT" in IGG™ for all grid patches belonging to a rotor/stator interface. The initialization process can be performed in two ways: 3. • A steady state initialization is performed in a separate computation with Steady as Time Configuration. The unsteady phase-lagged computation is using the result of this steady computation as initial solution. See Chapter 9 for more information on how to start a computation from an initial solution file. • The steady state initialization is automatically performed before starting the time accurate computation (that means within the same computation), switching to Unsteady as Time Configuration in the Flow Model page and selecting in the interface an appropriate Number of Steady Iterations in the Steady Initialization parameters on the Control Variables page. 4. The Number Of Angular Positions defined in the Control Variables page is the number of time steps per full revolution (2π) of the rotor. In theory, the number of time steps per full rotation has to be a multiple of the number of blades in the rotor (Nbrotor) and number of blades in the stator (Nbstator). Number Of Angular Positions = i x Nbrotor x Nbstator The two periods of blade passing frequencies are respectively (ixNbrotorxΔt) and (ixNbstatorxΔt). Since the number of time steps per passage is usually imposed around 40, the value of i should be adjusted so that (ixNbrotor) and (ixNbstator) are both close to this number. By experience, if the number of time steps per passage is lower than 30 the solution starts to be deteriorated. 5. The Number Of Time Steps in the Control Variable page is defined as: Number Of Time Steps = j x (Number Of Angular Positions)/min(Nbrotor,Nbstator) During the calculation, it is recommended to repeat the longer period at least 15 to 20 FINE™/Turbo 8-15 Dedicated Turbomachinery Models Rotor/Stator Interaction times (j evolves from 15 to 20). By experience, usually after 20 times (j=20), the flow becomes periodic. There is thus no need to make many full rotations and sometimes even one full rotation. 6. For more info on the Outputs Files available in the Control Variables page, see section 6-3.1. By default, the Phase Lagged method computes the viscous fluxes at the rotor/stator interface by extrapolation from dummy cell values, set from same side inner cells. c) Output When a simulation using the phase lagged method is performed, the output includes only one channel for each blade row. FINE™/Turbo provides a tool repetition, which allows the user to generate 3 channels for each blade row for post-processing. This tool can only be launched from the shell. On Linux: repetition project-path/project-name.run On Windows: Installation path\bin\repetition.exe project-path/project-name.run Then a new .run file "project-name_rep.run" and the corresponding .cgns files "projectname_rep_t##.cgns" will be generated. The user can load these files into CFView™ for postprocessing. d) Expert Parameters The following expert parameters can be used with an unsteady computation using phase lagged method: ICYOUT(integer): 1 is used in combination with Multiple Files option to avoid overwriting of the output files at each blade passage. RELPHL(real): 0.5 (default) if necessary, under-relaxation factor can be applied on Periodic and R/S boundary conditions by reducing the two values of the expert parameter for respectively the periodic and the R/S boundary conditions. 8-3.2.5 Harmonic Method The harmonic method provides unsteady flow results with considerably less constraints than the domain scaling and phase-lagged methods. More information on Harmonic method can be seen in section 8-4. a) Mesh Constraints Like the phase-lagged approach, it is necessary to set the grid patches of a rotor/stator interface to the boundary condition type "ROT". No specific azimuthal position of the blade channels is requested by the harmonic method, but it is recommended to have an overlapping region in the circumferential direction between the rotor and the stator channel. This is only for post-processing purposes. Visualization of the flow across the interface is much clearer. Mesh resolution in the tangential direction: The harmonic method is based on the spatial Fourier decomposition of the time-averaged flow and the harmonics in the tangential direction. 8-16 FINE™/Turbo Rotor/Stator Interaction Dedicated Turbomachinery Models It is suggested to guarantee at least 30 grid nodes in the azimuthal direction to represent in space the first harmonic (or fundamental) of a periodic disturbance at the inlet/outlet of a row. Then, the number of nodes in the tangential direction of the row channel should be at least 30 times the number of blades of the adjacent blade row generating this harmonic divided by the number of the blades of the row. The narrower the adjacent blade row channels, the more refined the channel should be. It is assumed that the amplitude of the subharmonics decreases very quickly. The constraint can thus be relaxed for the other harmonics. In general, at least 30 grid notes for the first harmonic and 15 for the other harmonics are suggested. For example, for a stator/rotor/stator configuration, where the number of blades in the rotor and stators are Nbrotor, Nbstator 1 and Nbstator 2 and NH is the number of harmonics: Number of Points in Azimuthal Direction in stator 1: Nb rotor 30 x --------------------Nb stator1 if(NH=1) Nb rotor - x NH if(NH>1) 15 x -------------------Nb stator1 Number of Points in Azimuthal Direction in rotor: Nb stator1 Nb stator2 - , 30 x -------------------- ) if(NH=1) max(30 x -------------------Nb rotor Nb rotor Nb stator1 Nb stator2 - x NH, 15 x -------------------- x NH) if(NH>1) max(15 x -------------------Nb rotor Nb rotor Number of Points in Azimuthal Direction in stator 2: Nb rotor 30 x -------------------Nb stator2 if(NH=1) Nb rotor - x NH if(NH>1) 15 x -------------------Nb stator2 b) FINE™/Turbo Settings 1. The harmonic method is a hybrid method. Unsteady flow results are obtained by the solving of pseudo-steady transport equations like in steady flow simulation. These pseudo-steady transport equations are solved for the time-averaged flow and for the harmonics of the periodic unsteady disturbances about the time-averaged flow. The Time Configuration in the Flow Model page should be set to Harmonic. 2. Under the Rotor-Stator tab of the Rotating Machinery page, the type of rotor/stator treatment is automatically selected. The full non-matching technique is used like in a mixing-plane simulation. However, the mixing-plane method is used only for the time-averaged Spalart-Allmaras eddy-viscosity. In particular, it includes a part of the deterministic stress that appears because of the time-averaging of the advective fluxes of the eddy-viscosity transport equation. All the other FINE™/Turbo 8-17 Dedicated Turbomachinery Models Rotor/Stator Interaction flow variables are treated by a connection algorithm based on the spatial Fourier decomposition of the time-averaged flow and the harmonics. The user has to specify for each of the patches the ID and the upstream/downstream location as described in section c) at step 2. 3. The initialization should be performed using a solution in steady state. The user can perform a separate computation (initial solution) for which the Time Configuration is set to Steady. For this computation, it is suggested to model the rotor/stator interface using the Non Reflecting 1D treatment. The result of this computation is used as the initial solution for the harmonic run. See Chapter 9 for more information on how to start a computation from an initial solution file. The user can also impose an appropriate Number of Steady Iterations in the Computation steering / Control Variables page. In this case, a steady computation will be performed until the Number of Steady Iterations in the fine mesh. Then the NLH computation will be initialized using the steady solution and be launched. NLH does not work when the rotor-stator interface is connecting two stators. c) Illustrative Example Results obtained from harmonic calculations using three harmonics. FIGURE 8.3.2-10 Aachen Turbine: entropy at 50% spanwise 8-3.2.6 Control the flux of Eddy viscosity For the Spalart-Allmaras turbulence model, the flux at the Rotor/Stator is computed using the pitch averaged eddy viscosity. Such a procedure can leads to a build-up of turbulence for multistage machineries. The eddy viscosity is not destroyed in the free stream. Very high level of eddy viscosity is often found in the last stages for multi-stage calculations. Such a high level of eddy viscosity can impact on the predicted efficiency of the machinery. Two methods can be used to reduce the eddy viscosity at a Rotor/Stator interface when using the Spalart-Allmaras model: • Control the flux of eddy viscosity at all rotor/Stator interfaces by using the minimum eddy viscosity over the pitch (IMINRS set to unity) • Control the flux of eddy viscosity at all rotor/Stator interfaces by multiplying the flux by a factor (FACTRS set lower than unity) 8-18 FINE™/Turbo Harmonic Method Dedicated Turbomachinery Models Because both the expert parameters are global, the limitation of the eddy viscosity at Rotor/Stator interfaces is activated for all Rotor/Stator interfaces of the project. Both methods cannot be combined. If the two parameters are changed only IMINRS will be activated. The methods reducing the eddy viscosity are restricted to the following Rotor/Stator interfaces: • Conservative coupling • Local conservative coupling • Full non matching mixing plane • Non reflecting 1D • Full non matching (non Reflecting) for NLH calculations 8-4 Harmonic Method 8-4.1 Introduction An attractive feature of FINE™/Turbo is the computation of unsteady flows using the so-called nonlinear harmonic method (NLH). This approach, introduced by He and Ning (1998), can be considered as a hybrid method that conjugates the advantages of classical steady state and full unsteady calculations: it provides an approximate unsteady solution at affordable calculation costs. The main idea is that the flow perturbations that make the flow unsteady are written about a timeaveraged value of the flow and are Fourier decomposed in time. Casting the unsteady NavierStokes system into the frequency domain, transport equations are obtained for each time frequency. The user controls the accuracy of the unsteady solution through the order of the Fourier series. Alongside the solving of the time-averaged flow steady-state equations, each frequency requires the solving of two additional sets of conservation equations (for the real and imaginary parts of each harmonic). The method is made nonlinear by the injection of the so-called deterministic stresses, resulting from all the solved frequencies, into the time-averaged flow solver. Because of the transposition to the frequency domain, only one blade channel is required like a steady flow simulation. The presented method also features an improved treatment that enhances the flow continuity across the rotor/stator interface by a reconstruction of the harmonics and the time-averaged flow on both sides of the interface. A non-reflective treatment is applied as well at each interface. The limitations for the NLH simulations are: • The nonlinear harmonic method can only be used for turbomachinery applications. • The Number of frequencies per perturbation and Max number of perturbations per blade row can not be larger than 10. And the product of them can not be larger than 20. • The flow perpendicular to the inlet (INL), outlet (OUT), external boundary (EXT) and rotor/ stator interface (ROT) has to be subsonic. • The number of frequencies per perturbation in a row is the same all over the multistage machine. • When using thermodynamic tables as fluid, NLH is not compatible with preconditioning and inlet distortion. • When simulating Cooling injectors with NLH, the injected mass flow is assumed constant. About the mesh constraint for NLH simulations, please refer to Chapter 8-3.2.5. FINE™/Turbo 8-19 Dedicated Turbomachinery Models 8-4.2 Harmonic Method Interface & Best Practice for Harmonic Computations When activating Harmonic in the Flow Model page, two boxes appear: • Number of frequencies per perturbation (number of harmonics: NBHAR): it represents the number of time harmonics per periodic perturbation modelled in a row. Default value: 3. • Max number of perturbations per blade row: the highest number of blade passing frequencies that a blade row is subjected to (NPERT). Default value: 2. For the particular stator/rotor/ stator configuration, where the stators have the same number of blades, this parameter is equal to 1. FIGURE 8.4.2-11 Harmonic parameters When Harmonic is checked, the turbulence model is by default set to Spalart-Allmaras. The other turbulence model that can be selected is Baldwin-Lomax. Euler flow.The Laminar flow can also be selected. The other harmonic method parameters in the FINE™/Turbo GUI can be found at the following menus: 8-4.2.1 Initial Solution It is recommended to set the initial solution as the result of a previous steady flow simulation. This improves the rate of convergence to the values of the amplitudes of the disturbance frequencies. 8-4.2.2 Boundary conditions For one stage or multi-stage computations, different boundary conditions can be specified for the NLH method. These boundary conditions are non-reflective at the far inlet and far outlet. They are based on 1D non-reflective treatment that computes the flow variables on the boundary as a resulting combination of incoming and outgoing characteristics. The flow at the far inlet and far outlet is assumed to be the time-averaged without the deterministic stress terms. Under the tab INLET of the Boundary Conditions page, a dedicated boundary condition, Static Quantities Distributions for Harmonic Calculation, allows FINE™/Turbo to perform NLH computations with distortion at inlet. For this kind of computations, the FINE™/Turbo solver performs a spatial Fourier decomposition of the inlet distortion. The extracted spatial harmonics are transformed into time harmonics in the frame of the domain that is subject to the relative motion of the distortion. This inlet boundary condition can be considered as a simplified Rotor-Stator interface. But the computation only takes into account the effect of the fictitious upstream row (inlet distortion) on the downstream row(s). With inlet distortion, it is possible to simulate the flow in only one row by using the NLH method. The inlet distortion must be specified by using profile. These profiles are the azimuthal distributions of the five flow variables ( v r , v t , v z , ρ and p ). Each distribution is for a constant radius or a constant axial position. The imposed profile must range from 0 to 2π and must be periodic over the azimuthal length. Currently, only r-θ or θ-z profile is allowed. The profile should be given at stations of constant θ for increasing r or z. Also θ must be increasing going from one station to the next in the file. Please refer to Appendix A-5 for more detail of the file format. The option PERIODICITY is used to scale the inputted profile in θ direction. 8-20 FINE™/Turbo Harmonic Method Dedicated Turbomachinery Models Under the tab EXTERNAL of the Boundary Conditions page, the user can specify external boundary conditions for NLH computations: • When using the boundary condition External, the flow at the external boundaries must be axial ( v x = 0 and v y = 0 ) if the external boundaries are attached to the rotating domain. • If the external boundaries are attached to the rotating domain and the flow at the external boundaries is non-axial, the boundary condition External Constant Wind with Incidence Relative to Axis Z should be used. This boundary condition allows to simulate the flow resulting from a constant wind with incidence applied on the external boundaries. The incidence means that v x and/or v y are not equal to 0. In the cylindrical framework, the velocity components write as: v t = – v x sin ( θ ) + v y cos ( θ ) v r = v x cos ( θ ) + v y sin ( θ ) (8-1) So, the incidence can be considered as a distortion on the external boundaries with the periodicity of 1. The same treatment method for inlet distortion is used to treat the incidence on the external boundaries in the flow solver. Note, the pseudo-steady solution in the NLH method represents the time-averaged solution over one passage. As a result, in the cylindrical framework, the incidence can not be represented since it is not periodic over one blade passage. To check the effect of the incidence, unsteady solution must be reconstructed. The boundary condition External Constant Wind with Incidence Relative to Axis Z is exclusively for external boundaries attached to rotating domains. 8-4.2.3 Outputs The Harmonics tab allows to activate specific outputs from the harmonic method and the reconstruction in time. FINE™/Turbo 8-21 Dedicated Turbomachinery Models Harmonic Method FIGURE 8.4.2-12 Harmonic outputs a) Harmonic variables output In the Harmonics page of the Outputs/Computed Variables page, a first group is visible and corresponds to the harmonic variables: • Static quantities: Temperature, Pressure, Density and Entropy • Total quantities: Relative Pressure, Absolute Pressure, Relative Temperature and Absolute Temperature. • Velocity components: vx , v y , vz If a box is checked, the Real & Imaginary parts and/or the norm (Amplitude) of the complex amplitude of the harmonics of the variable, can be stored in the output ".cgns" file. The number of harmonics is the maximum, over the whole flow field, of the total number of harmonics per group (blade row), which is equal to (NPERT)x(NBHAR), both set in the Flow Model page. Example 1: if the Pressure box is checked, there will be 6 harmonics of pressure fluctuation per row in the output solution file for NBHAR=3 and NPERT=2. This means 6 (for real) + 6 (for imaginary) + 6 (for norm) = 18 additional flow variables in the ".cgns" file, if the real and imaginary parts are selected as well as the norm. Example 2: For a igv/rotor/ogv configuration, NPERT is set to 2 and NBHAR is set to 4 by the user. There are thus 8 (2x4) harmonics H1, H2, H3, H4, H5, H6, H7, H8 in the output. • In igv row: only one perturbation is generated, induced by the downstream rotor. The perturbation is modelled by its first NBHAR=4 harmonics: H1-H2-H3-H4. No second perturbation exists, so H5, H6, H7, H8 are set to zero. • In rotor row: two perturbations are generated. If the first perturbation is the one originating from the row upstream then: 8-22 FINE™/Turbo Harmonic Method Dedicated Turbomachinery Models H1-H2-H3-H4: first 4 harmonics of the periodic disturbance induced by the igv, H5-H6-H7-H8: first 4 harmonics of the periodic disturbance induced by the ogv. • In ogv row: one perturbation is modelled, the first 4 orders being solved. H1-H2-H3-H4: first 4 harmonics of the periodic disturbance induced by the rotor. H5-H6-H7-H8: zero. In this case, selecting only the amplitude of the Pressure fluctuation for the output gives 8 additional flow variables in the ".cgns" file. If the relative/absolute total pressure or/and the relative/absolute total temperature time means are selected, then their harmonics will be automatically stored in the ".cgns" file, and vice-versa. A second group proposes the selection of the deterministic stresses. ( ρV x' )V x', ( ρV x' )V y', ( ρV x' )V z' ( ρV y' )V x', ( ρV y' )V y', ( ρV y' )V z' ( ρV z' )V x', ( ρV z' )V y', ( ρV z' )V z' ( ρV x' )H', ( ρV y' )H', ( ρV z' )H' If a stress is selected, each of its contribution per harmonic will be stored in the output ".cgns" file, that is 8 different values in example 2 presented above. Information about frequency output for harmonics can be found in the .std file for each group. Each group indicates a blade row. b) Plot3D output The Harmo2Time executable checks the .run file of the computation to process. If the plot3d output of the solver is switched on, the Harmo2Time executable will also produce unsteady plot3d output in addition to the .cgns output. As for the FINE™/Turbo solver, there are different options to the plot3d output: • The user can choose between ASCII and binary (formatted) output. • The user can choose to compute the plot3d output to be in relative or absolute frame of reference. The format of the plot3d output is the same as the FINE™/Turbo solver’s (see section 10-2.7). This output is only valid with IVELSY=1, which is also the only accessible option for the Harmo2Time executable. This plot3d output is limited to the perfect gas model. c) Reconstruction in Time The executable Harmo2Time for reconstructing a harmonic solution in time, is available in the Modules menu. It can be also launched from the command line: On UNIX/LINUX: FINE™/Turbo 8-23 Dedicated Turbomachinery Models harmo2time /full path/computation.run Harmonic Method On UNIX/LINUX On 32bits WINDOWS: \fine \bin\harmo2time.exe \full path\computation.run On 64bits WINDOWS: \fine \bin64\harmo2timex86_64.exe \full path\computation.run Harmo2Time generates a run file named "_unst.run" presenting the same format as for the result of an unsteady flow simulation. In the Harmonics tab of the Outputs/Computed Variables page, an extra control is available for the unsteady reconstruction, see Figure 8.4.2-12. The following parameters are only used for the Harmo2Time module and can thus be modified after the harmonic computation has finished: For the standard harmonic simulation (no clocking), the user can only reconstruct the unsteady flow. • Number of harmonics per perturbation used: The number of harmonics per perturbation that the user wants to keep for the reconstruction. By default, this parameter is set to the value of the Number of frequencies per perturbation that was chosen by the user in the Flow Model page. The number of harmonics per perturbation, used for the reconstruction in time, can be lower or equal to the value set in the Flow Model page. • Number of time steps: The number of instantaneous solutions per maximum blade passing period. By default, 10 instantaneous solutions ("_unst_t#.cgns" files) are generated whose time span extends over the maximum blade passing period of the multistage turbomachine. • Extract the solution in time at nodes: Offers the possibility to select different grid nodes in the mesh blocks at which the flow time evolution will be calculated. The program of reconstruction will generate one data file per grid node (_unst_P#.dat) that will include the evolution in time of the flow variables (density, pressure, velocity and also the eddy viscosity for a turbulent flow). In the frame of Rotated rows and number of channels, the user can specify the following parameters for every Block or Group for the reconstruction in time. • Number of channels represented: The number of repetitions of the channels that the user wants to use in the post-processing. • Displacement of the pitch: The user can specify a rotation of the blade row as a multiple of the pitch of the blade row. The inputted number must be an integer. For example, 2 [pitch] will rotate a blade row by twice 360deg/N where N is the periodicity of the blade row. By default, Harmo2Time automatically reconstructs the unsteady solutions for the following quantities, whatever the selected quantities in the Outputs / Computed Variables page are. • Static Pressure • Static Temperature • Density • Relative Velocity (Wxyz) When modelling turbulence, the turbulent viscosity (μt/μ) is outputted by Harmo2Time. Please note, the turbulent viscosity is computed by using the time-mean solutions and assumed undisturbed by the unsteady fluctuations. In addition, Harmo2Time will also reconstruct the unsteady solutions for the following quantities, in case that the corresponding quantities are selected for output in the Outputs / Computed Variables page. 8-24 FINE™/Turbo Harmonic Method Dedicated Turbomachinery Models • Absolute Total Pressure • Relative Total Pressure • Absolute Total Temperature • Relative Total Temperature 8-4.2.4 Control Variables In the Computation Steering / Control Variables page, the user can impose an Number of Steady Iterations. In this case, a steady computation will be performed until the Number of Steady Iterations in the fine mesh. Then the NLH computation will be initialized using the steady solution and be launched. NLH computations need more CPU time and memory, in comparison with a steady mixing-plane method, due to the additional transport equations associated with each harmonic. If N harmonics of a perturbation are to be modelled, then there are 10N transport equations to be solved (5 for the real part and 5 for the imaginary part of the complex amplitude of each harmonic). The CPU time required by harmonic method is: 10N CPU NLH = CPU steady CR N with CR N = 1 + ----------------N steady (8-2) where CPUsteady is the CPU time required by the steady computation and Nsteady is the number of the equations in the steady computation (5 for Euler, Laminar and turbulent flow with the 0-equation turbulence models; 6 for the turbulent flow with the 1-equation turbulence models). CR N is the cost ratio between the harmonic computation and the steady computation. For example, for a 3-harmonic simulation (N=3) and using the Spalart-Allmaras model ( Nsteady =6), the CPU time is therefore 6 times that of a steady simulation. The memory cost follows the same rule as Eq. 8-2. For the simulation of the multi-row flow through b1, ... ,bB bladerows, the cost ratio is approximated as: N nodes, b Cost N ( b ) + ... + N nodes, b Cost N ( b ) 1 1 B B CR harmo = -----------------------------------------------------------------------------------------------------------------N nodes, b + ... + N nodes, b 1 (8-3) B where N nodes, b1 is the number of the grid nodes in the bladerow b1, B is the number of the bladerows. As an approximation, the number of nodes can be assumed to be the same in the bladerows. The number of harmonics to be solved is N in the first bladerow and N in the last bladerow because only one perturbation is solved, generated from the downstream b2 and the upstream bB-1. The interior bladerows are subject to two perturbations, one generated from the upstream blade passing (wakes) and one generated from the downstream blade passing (potential effect). Therefore, 2N harmonics are solved in these bladerows. The estimated resulting CPU and memory cost ratios are: FINE™/Turbo 8-25 Dedicated Turbomachinery Models Harmonic Method 2Cost N + ( B – 2 )Cost 2N CR harmo = ------------------------------------------------------------B (8-4) 8-4.2.5 Troubleshooting in Rotor/Stator Interface Sometimes, the user may find that there is a quite large discontinuity in the variable field (such as entropy) over the rotor-stator interface, even when the number of harmonics per perturbation is 4 or more. This situation often appears if there exists a strong wake or shock wave at one side of the rotor-stator interface. Within the NLH method, the conservative variable is decomposed into a time-averaged value and a sum of periodic perturbations, which in turn are decomposed into N harmonics. In some special cases, the perturbation can not be accurately reconstructed by using the decomposed harmonics. The error is depending on the number of the harmonics that we used. Figure 8.4.2-13 shows how a square wave signal is captured by using a Fourier series (harmonics) and what the influence of the number of harmonics used is. Please refer to http://en.wikipedia.org/ wiki/Fourier_series for more information. As you can see, the square wave is reproduced better with an increasing number of harmonics. However, it is impossible to reproduce the vertical line in the signal. This can only be reached if the number of harmonics is infinite. 1h 3h 2h 4h FIGURE 8.4.2-13 The first four Fourier series approximations for a square wave As an example, Figure 8.4.2-14 shows the contours of the entropy at a constant r surface in a contra rotating propeller. In this case, there is a strong peak in entropy at the upstream side of the rotor-stator interface due to the wake of the front blade. This is almost a Dirac signal. To capture such a Dirac with Fourier series (that is what non-linear harmonics computations do) is indeed very difficult. As you can see, the signal is captured better when increasing the number of harmonics. This is in agreement with the theory: increasing the number of harmonics will increase the accuracy, but with increasing computation costs. 8-26 FINE™/Turbo Harmonic Method Dedicated Turbomachinery Models FIGURE 8.4.2-14 The 8-4.3 contours of the entropy at a constant r surface for a Contra-rotating propeller Expert Parameters 8-4.3.1 Expert Parameters for the Flow Solver The following expert parameter related to the NLH simulation are accessible on the Control Variables page by selecting the Expert Mode. HARTCL (integer):When using the Cooling/Bleed model with NLH, the time averaged variables in the cooling/bleed are computed by taking into account the deterministic stresses and the harmonic variables are computed by applying the non reflecting treatment. Adding the stresses implies that the harmonic values are already known but their computations with the non reflective treatment need the values of the time averaged variables. This is not a problem for the bleed as the time averaged values are extrapolated from the first inner cells. For the injectors, some assumptions are used for the computations of stresses. The main assumption is that the injected mass flow is constant with time. Moreover, the expert parameter HARTCL is used to impose the fluctuations of temperature or total temperature (according to the specified characteristics of the cooling). 0 (default): Harmonics of the temperature or total temperature are imposed to 0 in the injectors. 1: Harmonics of the temperature or total temperature are not imposed. Only the time averaged value is imposed. IFABCW (integer):On the wall, the velocity components, the pressure and the temperature in the dummy cell are computed by extrapolating the value on the wall and in the first inner cell. The corresponding density is computed in the dummy cell. The cooling will introduce high temperature gradient on the wall. The high temperature gradient may lead to unphysical temperature in the dummy cell and consequently unphysical density in the dummy cell. The expert parameter IFABCW allows to compute the density by extrapolating the density on the wall and in the first inner cell. The extrapolation is used not only for the time averaged values but also for the harmonic values. FINE™/Turbo 8-27 Dedicated Turbomachinery Models Harmonic Method 0 (default): the density in the dummy cell is computed from the extrapolated pressure and temperature in the dummy cell. 1: the density in the dummy cell is computed by extrapolating the density on the wall and in the first inner cell. IDECOU (integer):Controls if considering the deterministic stress terms when solving the timeaveraged equations. The deterministic stress terms are intrinsic to the nonlinear harmonic method and are responsible for the improvement of the time-averaged flow compared to simple linearization methods. In some cases, the deterministic stress terms are so high that convergence problem may appear. To reach the convergence, the deterministic stress terms can be removed from the time-averaged equations. An result is thus obtained for the time-averaged flow with less accuracy because the nonlinear term is removed. 0 (default): the deterministic stress terms are considered when solving the timeaveraged equations. 1: the deterministic stress terms will be removed when solving the time-averaged equations. HAVMOD (integer):In some computations, one can notice a strong gradient of the harmonic of the pressure. To control such a gradient, the flow solver uses a harmonic pressure sensor as it is done for the time-averaged solution. The time-averaged pressure sensor is: p i – 1 – 2p i + p i + 1 1 p˜ i – 1 – 2p˜ i + p˜ i + 1 psw = ---------------------------------------------- + --- ---------------------------------------------p i – 1 + 2p i + p i + 1 2 p i – 1 + 2p i + p i + 1 0 (default): no harmonic pressure switch. 1: using the following pressure sensor: p˜ i – 1 – 2p˜ i + p˜ i + 1 psw 1 = --------------------------------------------------------------------------------------------------------------------------------------------------( 1 – a 2 ) ( p˜ i – 1 – 2 p˜ i + p˜ i + 1 ) + a 2 ( p i – 1 + 2 p i + p i + 1 ) where a 2 is a constant controlled by the expert parameter HARAV2 (default value 0.01). The second term of the denominator is to keep the denominator different from zero and is chosen to be a percentage of the time-averaged static pressure. The pressure sensor will be activated when harmonic pressure gradient is very strong. 2: using the following pressure sensor: psw 2 = max ( psw, p sw 1 ) The pressure sensor will be activated when harmonic or time-averaged pressure gradients are very strong. 3: using the following pressure sensor: p˜ i – 1 – 2p˜ i + p˜ i + 1 psw 3 = max psw, --------------------------------------------------------------- a 2 ( p i – 1 + 2 p i + p i + 1 ) TDECOU (integer):Controls if considering the high order derivative when computing the thermodynamic variables by using thermodynamic tables: 0 (default): High order derivative is considered for thermodynamic variables. 1: High order derivative is not considered for thermodynamic variables. 8-28 FINE™/Turbo Harmonic Method Dedicated Turbomachinery Models When the expert parameter IDECOU=1, the expert parameter TDECOU will be set to 1 automatically, which means that high order derivative will not be considered for thermodynamic variables and the deterministic stress terms will not be considered when solving the time-averaged equations. 8-4.3.2 Expert Parameters for Reconstruction in Time The following expert parameter related to the reconstruction in time of a harmonic computation are accessible on the Control Variables page by selecting the Expert Mode. By default, Harmo2Time reconstructs an unsteady solution from the harmonic result by using all the harmonics or the first N harmonics, where N is the Number of harmonics per perturbation used inputted in the Outputs / Computed Variables page under the Harmonics tab. Harmo2Time can also partially reconstruct an unsteady solution by using certain harmonic(s) specified by the user. For example, the user can reconstruct an unsteady solution that includes only the contribution of the first and/or the second harmonic(s) of per perturbation. To perform a partial reconstruction, the user has to specify the Rows/Groups, where the unsteady solution will be partially reconstructed, through the expert parameter NHGALL. A maximum of 2 Rows/Groups can be selected at the same time. Then the user needs to specify the harmonic(s) through the expert parameters NHSUB and/or NHSUB2 for the Row1/Group1 and/or Row2/ Group2, respectively. NHGALL(integer):List of switches for the Groups. There are 20 parameters for the expert parameter NHGALL, which is corresponding to the Group index in the project (up to 20 Groups). The user can find the information of the Groups in the .std file in the project directory. For each switch: 0: the reconstruction in the corresponding Group will be partial. Only the specified harmonic(s) will be taken into account. 1 (default): the reconstruction in the corresponding Group will be full. The the first N harmonics will be taken into account, where N is the Number of harmonics per perturbation used inputted by the user. NHSUB(integer): List of switches for the harmonics in the first specified Group. There are 20 parameters for the expert parameter NHSUB, which is corresponding to the harmonic index per perturbation (up to 20). The numbers of the harmonics are listed in the .std file in the project directory. For each switch: 0: the corresponding harmonic will not be considered when reconstructing. 1 (default): the corresponding harmonic will be considered when reconstructing. For example, setting the second and the fourth values of the list to 1 means that the reconstructed unsteadiness is from the harmonics #2 and #4. NHSUB2(integer): List of switches for the harmonics in the second specified Group (if available). The setting of this parameter is the same with NHSUB. IGETBK(integer): switch for display mode of the rotating blade channel. When the rotor (visualized with multiple pitches) arrives at the position that is 1 period further away, it goes back to the original position. To make the rotor continue to move to the end of the reconstruction period before going back to the initial starting position, the user can set the expert parameter IGETBK to 2. FINE™/Turbo 8-29 Dedicated Turbomachinery Models Clocking 1(default): The following blade channel is represented in the reconstruction after displacement over more than one pitch 2: The same blade channel(s) are represented on the whole period of reconstruction. NBPPER(integer): controls the number of the blade passing periods built by Harmo2time. The user can modify it, such as a lowest common multiple of periods for all signals, in order to have a periodic signal. INDEXT(integer): defines an output range of time steps when reconstructing a harmonic solution in time. The parameter INDEXT is an array of two dimensions, corresponding to the first index t1 and the second index t2. If t 1 = 0 , all the time steps over NBPPER periods are outputted. If t 1 > 0 , the imposed time steps are outputted. PERVAR(integer): controls the output of Harmo2time. 0 (default): output the quantity (the time averaged value + perturbation) 1: only output the perturbation of the quantity IUNSMF(integer): allows to output unsteady ".mf" file at each time step by Harmo2time. The outputted ".mf" file has the same format with the one generated by the flow solver (see Chapter 10-2.6). 0 (default): does not output unsteady ".mf" file 1: output unsteady ".mf" file at each time step The following limitations exist when using IUNSMF=1: •Axial thrust, torque and power are assumed constant, and have the same values as in the steady ".mf" file. •Specific heat and specific heat ratio for real gas and incompressible fluid are assumed constant, and have the same values as in the steady ".mf" file. •Mach number for real gas is calculated by using time-averaged speed of sound. •Cooling and bleed mass flow are assumed constant, and have the same values as in the steady ".mf" file. •IWRIT larger than 2 is not supported. •OUTTYP equal 1 is not supported. 8-5 Clocking 8-5.1 Introduction The NLH method deals mainly with rotor/stator interaction. The approach couples and solves the time-averaged flow and the perturbations. In particular, the time-mean flow is modified by the deterministic stress that is a product of the unsteadiness. Thus, the time-mean solution in a row is influenced by the unsteadiness brought about by a rotating upstream row; by relative rotation this flow disturbs the flow in a downstream row again. The upstream row has an influence on the downstream row via the time-mean flow in the central row but it is indirect. No rotor/rotor and/or stator/ stator effects are taken into account. Thus, the clocking effects cannot be modelled 8-30 FINE™/Turbo Clocking Dedicated Turbomachinery Models The present Clocking model allows the user to simulate the clocking effects between consecutive rotors or stators. The range of influence is 1.5 stage upstream or downstream: for a multistage machine row1/row2/row3/row4/row5 the following clocking interactions are modelled: row1row3; row3-row5, row2-row4. The clocking between row5 and row1 is not modelled. 8-5.2 Interface Settings FIGURE 8.5.2-15 Clocking settings The Clocking model can be switched on/off through the radio button Clocking on the Flow model page. When the Clocking model is switch on, a radio button switch appears in the expert parameters frame (visible only in Expert mode) to control the fixed or variable clocking. Variable: From this simulation, the user can reconstruct the unsteady flow for all the positions of the rows. For instance, one stator can be moved relatively to another stator and the unsteady flow can be reconstructed for each relative position. This simulation takes the effect of a rotor (respectively stator) onto the subsequent rotor (respectively stator) into account. In the post-processing the time-mean flow can be represented for all the different positions of one stator (or rotor) relatively to the subsequent stator (or rotor). Fixed: Same as "Variable" but with the difference that the stator (or rotor) can’t be moved in the post-processing. The effects from one stator onto the other stator are also taken into account but only for the position given in the input mesh. So it is like the standard harmonic but with the difference that the effects of stator1 onto stator2 are taken into account. In the post-processing the user can only reconstruct the unsteady flow. When Clocking is activated, the parameter Max number of perturbations per blade row includes the clocking perturbations. For example, for the row1/row2/row3 configuration, this parameter is equal to 2. However, for the row1/row2/row3/row4/row5 configuration, this parameter should be equal to 4. FINE™/Turbo 8-31 Dedicated Turbomachinery Models Clocking 8-5.2.1 Reconstruction in Time The program Harmo2Time for reconstructing a harmonic solution in time or in space, is also available for clocking simulations. All the settings in the Harmonics tab of the Computed Variables page are the same as describing in Chapter 8-4.2.3, except the following settings that are special or dedicated to clocking simulations. In the Harmonics tab of the Computed Variables page (seen in Figure 8.5.2-16), the user has two possibilities for reconstruction in time when the harmonic result simulates the clocking effects. FIGURE 8.5.2-16 Harmonic outputs in case of clocking considered • Instantaneous flow: Reconstruct unsteady flow like the standard harmonic output. For each blade row, the user can change its relative clocking position by specify the Displacement of the pitch in the frame of Rotated rows and number of channels. The inputted number can be a real number. For example, 0.5 [pitch] will rotate the blade row by a half of a pitch (360deg/N where N is the periodicity of the blade row). • Time mean flow = f(clocking): Reconstruct time-mean flow varying with the position of the selected blade row or distortion. For each blade row, the user can change its relative clocking position by specify the Displacement of the pitch in the frame of Rotated rows and number of channels. The inputted number 8-32 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models can be a real number. For example, 0.5 [pitch] will rotate the blade row by a half of a pitch (360deg/N where N is the periodicity of the blade row). The option Variable Clocking must be activated for one of all rows or the inlet distortion. By default, the option Variable Clocking is activated for the first row in the Blocks&Groups list. The parameter Number of positions, which appears if Variable Clocking is activated, is used to set the number of clocking positions over the 100% pitch displacement. When launching Harmo2Time, the time-mean flow will be reconstructed for each clocking position of the selected blade row. As an illustration of the reconstruction of time mean flow = f(clocking), the Aachen turbine case is shown in Figure 8.5.2-17. In this case, the row3 is set as Variable Clocking and the Number of positions is set to 4. The time mean flow is reconstructed at four clocking positions of the row3. The option Time mean flow = f(clocking) is only available for a variable clocking simulation. If the button Variable Clocking is switched on for a block or group, then it is switched off for all the other blocks or groups. FIGURE 8.5.2-17 Reconstructed time mean flow varying with the different clocking positions of the row3 in the Aachen turbine case 8-6 Cooling/Bleed 8-6.1 Introduction The Cooling/Bleed model allows both the simulation of cooling flows injected through solid walls into the flow or bleed flows where mass flow leaves the main flow through solid wall. The adopted technique makes use of additional sources of mass, momentum and energy located at given points or along given lines of the solid walls and does not require the meshing of the cooling flow injection channels. The objective of this model is not to describe the details of the cooling flow FINE™/Turbo 8-33 Dedicated Turbomachinery Models Cooling/Bleed itself but rather to consider its effect on the main flow. The major hypothesis of the model is that the injection/bleed surface is smaller than the local cell surface. In the next sections the following information is given on the Cooling/Bleed model: • section 8-6.2 describes how to set up a project involving the Cooling/Bleed model under the FINE™/Turbo user environment. • section 8-6.3 gives a summary of the available expert parameters related to cooling or bleed flow. • section 8-6.4 provides the format of the Cooling/Bleed input data file. 8-6.2 Cooling/Bleed Model in the FINE™/Turbo GUI The Cooling/Bleed model can be directly activated from the FINE™/Turbo interface by opening the Cooling/Bleed page under Optional Models. The layout of the page is shown in Figure 8.6.218. The list box on the top of the page (a) displays all the injectors (Cooling or Bleed) imported or added by the user. The buttons below the list (b) enable to Preview, Add, Edit, Remove, Import (more details on data file in section 8-6.4) injectors or Export injectors definitions to a file. The list box (c) gives the informations of total cooling/bleed mass flow. Clicking with the left mouse button on a selected injector will display its corresponding parameters in the lower part of the page (d). Clicking with the right mouse button on a selected injector will display a popup menu enabling to add/edit/remove the injector. The button Spreading of the hole on the top of the page can be used to control the location and spreading of the injector. When Spreading of the hole is switched off, the old algorithm of the cooling/bleed model will be used. A hole will be included in one cell only, even when the diameter of the hole exceeds the cell width. The hole center is the closest cell face center to the defined point. When Spreading of the hole is switched on, the new algorithm will be used. The position of the hole and slot is computed exactly. All cells included in the definition of the hole and slot will be used. And the hole or slot can spread over a patch border to another patch. The spreading of injector can only cross one border between patches. The spreading of injector is not implemented to cross a periodic boundary. 8-34 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models (a) (b) (c) (d) FIGURE 8.6.2-18 Cooling/Bleed page in FINE™/Turbo For the Points type of holes, two additional options are available: Number Of Periodic Repetitions and View Hole Tubes. If the mesh in the project is generated by AutoGrid5 and includes multiple blade passages in one row, the user may create or input the Points type of holes in one blade passage, then set the Number Of Periodic Repetitions to cover all the blade passages. The button View Hole Tubes is used to show the hole as a tube. When the user defines holes in AutoGrid5 template but does not mesh them, the hole line file or the geomTurbo file created by AutoGrid5 can be directly imported as a Points type of data file to define the injector. The system automatically selects all the patches related for each holes definition. To use this function, the grid configuration has to be activated when setting the information of the mesh. 8-6.2.1 Injector Sector Wizard When adding an injector (Add Injector button), for each injection the following parameters need to be specified through a wizard: • injector name, • injector role: Cooling or Bleed, • injector solid patches location, • definition of the geometry, • position of the injector, • flow parameters. FINE™/Turbo 8-35 Dedicated Turbomachinery Models Cooling/Bleed On the first page of this wizard the user can enter the name, the role, the solid patches, the geometry definition and the type of positioning of the injector. FIGURE 8.6.2-19 Injection Sector Wizard a) Injection Sector Name The name should be entered by moving the mouse to the text box for the Injector Name and to type the name on the keyboard. By default a name is proposed like "injector_1". It is strongly recommended to use only standard english letters, arabic numerals and underscore "_" symbol when naming an injection sector. Non-standard characters may not be recognized or may be misinterpreted when using the project on other computers. b) Injection Sector Role The role of the injector should be entered: Cooling if the flow is injected through solid walls into the main flow or Bleed if part of the mass flow leaves the main flow through solid walls. c) Injection Sector Geometry Three types of injection sectors can be defined through the interface: point, line or slot. • the Point type corresponds to a single cooling hole. • the Line type stands for a series of cooling holes regularly distributed along a line with the same geometrical and flow properties. • a hub or shroud Slot is a continuous line of holes placed at constant radius and axial position (typically used on the hub or shroud surface of a turbomachine). Slots are only defined along axisymmetric surfaces. In case a slot (or a line) should traverse several patches (as for instance in a HOH mesh configuration) all the patches should be selected and one single slot should be created. • For the Points type, the location of the cooling holes can be defined with a list of points defined by the user. The definition of the holes will no longer be related to the topology of the mesh, but to the geometrical entities including hub, shroud and blades. 8-36 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models d) Injection Sector Positioning Four modes are available to place the holes: • Relative mode: this mode is used for blade walls and is valid for AutoGrid™ meshes only. In this case, the spanwise and streamwise positions of the hole (or of the 2 extremities in the case of a line of holes) are specified. • Space Cartesian mode: the user specifies the (X,Y,Z) Cartesian coordinates of the hole or of the 2 extremities for a line. For a slot the user enters the radius and the Z-coordinate of one point of the slot. • Space Cylindrical mode: the user specifies the (R,θ,Z) cylindrical coordinates of the hole or of the 2 extremities for a line. For a slot the user enters the radius and the Z-coordinate of one point of the slot. • Grid mode: the user specifies the (I,J,K) indices of the hole or of the 2 extremities of a line of holes. The injection sectors of type Slot cannot be presented in relative coordinates. The combination of injector geometry and positioning can be summarized as follows: FIGURE 8.6.2-20 Injector sector geometry/positioning combination & restriction To cancel the modifications to the injector definition and close the wizard click on the Cancel button. Once the injector sector role, type and mode are correctly set, click on Next>> to go to the next page of the wizard. On this page, depending of the role, type and mode of injector, the flow parameters and geometry/positioning parameters have to be defined in the second page of the wizard. When defining a cooling or bleed using the Cartesian or cylindrical coordinates, no procedure is implemented to check if the specified direction is correct. e) Injection Sector Geometry/Positioning Parameters As presented in Figure 8.6.2-20, 12 combinations are available. As the transformation from cylindrical to Cartesian coordinates is obvious, only 9 combinations will be described in more detail. e.1) Relative positioning for a single hole The user specifies the diameter of the hole in case of a single hole. Each hole is circular. The diameter of the hole is used to calculate the outgoing velocity. FINE™/Turbo 8-37 Dedicated Turbomachinery Models Cooling/Bleed As for the old algorithm, the holes are located by means of a spanwise and a streamwise relative position. The algorithm can be applied to H, I or O-meshes generated by AutoGrid™. For Omeshes the blade surface is divided in two different sub-patches (one for the pressure side and one for the suction side). Therefore, the user has to select on which side of the blade (Side1/Side2) the injection will be located. A button has been added in the interface in order to select the side. This button is active only for O-meshes. Only AutoGrid™ provided with FINE™/Turbo 6.1-1 (and later versions) can be used to generate the mesh and this relative positioning is only available for blade surfaces. FIGURE 8.6.2-21 Geometry parameters for relative positioning of a hole The location is defined as a fraction of the arc length from hub to shroud and from the leading edge to the trailing edge. Spanwise and streamwise coordinates are computed for each cell vertex. The closest point found in this relative coordinate frame is the one that is concerned by the injection. An option has been set-up in order to use the axial chord (Axial Coordinates option) instead of the arc length (only available for axial machines). The relative positioning does not accept meshes with a blunt at the leading edge A pop-down manu Select positioning patch is added in the interface. The user has to choose the patch that the hole will be positioned. Finally, three ways to impose the injection direction are proposed through the interface: Cartesian, cylindrical or grid indices. For injection direction specified in Cylindrical coordinates two options are available: it can be defined in the relative frame of reference or in the absolute frame of reference. 8-38 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models FIGURE 8.6.2-22 . Relative positioning of a hole at 70% spanwise and 50% streamwise. When Grid Indices is selected, the injection direction is provided by the user through 2 angles expressed in degrees (depending of the units selected in the menu File/Preferences). Each angle is measured with respect to the local normal and one of the 2 grid line directions tangent to the wall. ( J, K ) I In case of an J = ct surface, the angles are measured with respect to the ( K, I ) grid lines respec( I, J ) K st tively. Figure 8.6.2-23 illustrates the definition of angle βk for an I = c surface. I=constant surface V J K βk n βk is the angle of the velocity projection in the (K,n) plane with respect to the normal n to the surface. FIGURE 8.6.2-23 Angle definition in the cooling flow page of the FINE™ GUI Each angle is defined as: V i, j, k β i, j, k = atan ------------- Vn (8-5) For example, in order to make the velocity direction oriented along the normal, the two angles should be set equal to 0. A 90 degrees angle is not allowed as it will induce a velocity vector tangent to the corresponding grid line direction, with zero mass flow. FINE™/Turbo 8-39 Dedicated Turbomachinery Models Cooling/Bleed For holes located on the blade walls and when the mesh is generated with AutoGrid™, the K- and J- lines are the two tangent directions along the blade wall, respectively oriented in the streamwise and spanwise directions. e.2) Relative positioning for a line of holes The user specifies the diameter of the hole in case of a line of holes. Furthermore, the number of holes has to be specified and will be uniformly distributed on the line. Each hole is circular. The diameter of the hole is used to calculate the outgoing velocity. As for the old algorithm, the line of holes is defined by two points (holes) that are located by means of a spanwise and a streamwise relative position. The algorithm can be applied to H, I or O-meshes generated by AutoGrid™. For O-mesh the blade surface is divided in two different sub-patches (one for the pressure side and one for the suction side). Therefore, the user has to select on which side of the blade (Side1/Side2) the injection will be located. A button has been added in the interface in order to select the side. This button is active only for O-meshes. For each point of the line the algorithm works as for the single hole positioning. FIGURE 8.6.2-24 Geometry parameters for relative positioning of a line of holes Only AutoGrid™ provided with FINE™/Turbo 6.1-1 (and later versions) can be used to generate the mesh and this relative positioning is only available for blade surfaces. The location is defined as a fraction of the arc length from hub to shroud and from the leading edge to the trailing edge. Spanwise and streamwise coordinates are computed for each cell vertex. The closest point found in this relative coordinate frame is the one that is concerned by the injection. A pop-down manu Select positioning patch is added in the interface. The user has to choose the patch that the hole will be positioned. And an option has been set-up in order to use the axial chord (Axial Coordinates option) instead of the arc length (only available for axial machines). The relative positioning does not accept meshes with a blunt at the leading edge Finally, three ways to impose the injection direction are proposed through the interface: Cartesian, cylindrical or grid indices. When Grid Indices is selected, refer to the end of section e.1) for more details. For injection direction specified in Cylindrical coordinates two options are available: it can be defined in the relative frame of reference or in the absolute frame of reference. 8-40 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models e.3) Cartesian positioning for a single hole The user specifies the diameter of the hole in case of a single hole. Each hole is circular. The diameter of the hole is used to calculate the outgoing velocity. As for the old algorithm, the holes are located by means of the (X,Y,Z) Cartesian coordinates. For a single hole, the cell that is concerned by the injection is the closest cell face centre to the defined point. In case of repetition, the point is automatically transferred to the meshed patch Furthermore, in order to ease the capture of the right coordinates, the button Get Coordinates enables the user to interactively select the point in the mesh view after opening the mesh through the menu Mesh/View On/Off or Mesh/Tearoff graphics (only available on UNIX). FIGURE 8.6.2-25 Geometry parameters for space Cartesian positioning of a hole A pop-down manu Select positioning patch is added in the interface. The user has to choose the patch that the hole will be positioned. Finally, three ways to impose the injection direction are proposed through the interface: Cartesian, cylindrical or grid indices. When Grid Indices is selected, refer to the end of section e.1) for more details. For injection direction specified in Cylindrical coordinates two options are available: it can be defined in the relative frame of reference or in the absolute frame of reference. e.4) Cartesian positioning for a line of holes The user specifies the diameter of the hole in case of a line of holes. Furthermore, the number of holes has to be specified. Each hole is circular. The diameter of the hole is used to calculate the outgoing velocity. As for the old algorithm, the line of holes is defined by two points (holes) that are located by means of the (X,Y,Z) Cartesian coordinates. For the two points defining the line, the cells that are concerned by the injection are the closest cell face centre to the defined point. In case of a repetition, the point is automatically transferred to the meshed patch Furthermore, in order to ease the capture of the right coordinates, the button Get Coordinates enables the user to interactively select the point in the mesh view after opening the mesh through the menu Mesh/View On/Off or Mesh/Tearoff graphics (only available on UNIX). FINE™/Turbo 8-41 Dedicated Turbomachinery Models FIGURE 8.6.2-26 Geometry Cooling/Bleed parameters for space Cartesian positioning of a line of holes A line is drawn from those two points (this line does not necessarily follow the surface of the patch, see Figure 8.6.2-27). The segment is then uniformly divided into N-1 sub-segments (where N is the number of holes on this line). Each N-2 limits of the sub-segment is then projected on the patch (the closest cell face centre is found). Those are the cells where the injection will be applied. They are not necessarily uniformly distributed on the patch. points defined by user points at cell face centre where injection will be applied FIGURE 8.6.2-27 Construction of a line of holes on a turbine hub For a mesh with a high clustering, or for a high number of points on the line, several projected points could end on the same cell. This is taken into account in the algorithm. The mass flow injected is then multiplied by the relevant factor. Therefore, one should be aware that the number of cells that are highlighted in the interface should not strictly match the number of holes on the line On the contrary for a mesh with a relatively poor spatial discretization, the location of the cell face centres where the injection will be applied will not be strictly on a line. A limitation of this algorithm is that the line does not necessarily follow the patch surface. Therefore, defining a line of holes at the hub of a gap (upper surface of a rotor blade) could produce the problem presented on the left side of Figure 8.6.2-28. The same problem can arise generally on a convex surface. In order 8-42 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models to solve this problem, the user can define a line of holes following a parametric surface defined by the grid lines by activating Parametric Space. Therefore, a line of holes on a convex surface could be more easily defined (right side of Figure 8.6.2-28).. within Parametric Space without Parametric Space FIGURE 8.6.2-28 Definition of a line of holes without or within the parametric space One limitation of this option is that a line of holes cannot cross a connection. For instance defining a line of holes (in the parametric space) close to the trailing edge of a O mesh will produce the result sketched bellow. POSSIBLE FIGURE 8.6.2-29 Definition FINE™/Turbo of a line of holes in the parametric space. 8-43 Dedicated Turbomachinery Models Cooling/Bleed For turbomachinery configuration with periodic conditions, points could be located either on the meshed passage or on one of its repetitions. Therefore, the injections are automatically transferred to the meshed patch. FIGURE 8.6.2-30 Two methods to respect repetition for a line of 3 holes. In case of multi-patch selection the algorithm described above is applied independently for each patch. Therefore, a direct definition of a line of holes crossing several patches is not possible. In this case it is recommended to define as many lines as necessary (see figure below). In order to overcome this problem the multi-patch selection has been restricted to the slots defined by Cartesian or cylindrical coordinates. FIGURE 8.6.2-31 Example of definition of a line of 5 holes with multi-patch selection. A pop-down manu Select positioning patch is added in the interface. The user has to choose the patch that the hole will be positioned. Finally, three ways to impose the injection direction are proposed through the interface: Cartesian, cylindrical or grid indices. When Grid Indices is selected, refer to the end of section e.1) for more details. For injection direction specified in Cylindrical coordinates two options are available: it can be defined in the relative frame of reference or in the absolute frame of reference. 8-44 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models e.5) Cartesian positioning for Points of holes The user specifies the diameter of the hole in case of points of holes. Each hole is circular. The diameter of the hole is used to calculate the outgoing velocity. For the points type of holes, the positioning patches are not required any more. The user inputs the center coordinates and the injection direction for each hole by means of the (X,Y,Z) Cartesian coordinates. The button Add Hole allows to add a hole in the list. A double click will be necessary to access the input of the center coordinates and the injection direction of the hole. The button Remove Holes allows to remove the selected holes. Another button Reverse Axis will reverse the injection direction for all the selected holes. FIGURE 8.6.2-32 Geometry parameters for space Cartesian positioning of points of holes e.6) Grid positioning for a single hole The user specifies the diameter of the hole in case of a single hole. Each hole is circular. The diameter of the hole is used to calculate the outgoing velocity. The grid positioning used in the FINE™/Turbo solver depends on the grid indices of the centre of the cell faces. It is different from the grid indices used in IGG™ and in CFView™. The grid indices are directly used by the flow solver in order to introduce the flow of mass, momentum and energy at this cell face. FIGURE 8.6.2-33 Geometry Parameters for Grid positioning of a hole A pop-down manu Select positioning patch is added in the interface. The user has to choose the patch that the hole will be positioned. FINE™/Turbo 8-45 Dedicated Turbomachinery Models Cooling/Bleed Finally, three ways to impose the injection direction are proposed through the interface: Cartesian, cylindrical or grid indices. When Grid Indices is selected, refer to the end of section e.1) for more details. For injection direction specified in Cylindrical coordinates two options are available: it can be defined in the relative frame of reference or in the absolute frame of reference. e.7) Grid positioning for a line of holes The user specifies the diameter of the hole in case of a line of holes. Furthermore, the number of holes has to be specified. Each hole is circular. The diameter of the hole is used to calculate the outgoing velocity. From the two cell face centres defined in the interface, two geometrical points are defined by their (x,y,z) coordinates. Then, a line is constructed in the same way as for the Cartesian positioning (section e.4). In this case there is no problem of repetition because the two extremities of the line are located on the meshed patch. Furthermore, concerning the Parametric Space option, refer to section e.4) on page 7-24 for more details. FIGURE 8.6.2-34 Geometry parameters for Grid positioning of a line of holes A pop-down manu Select positioning patch is added in the interface. The user has to choose the patch that the hole will be positioned. Finally, three ways to impose the injection direction are proposed through the interface: Cartesian, cylindrical or grid indices. When Grid Indices is selected, refer to the end of section e.1) for more details. For injection direction specified in Cylindrical coordinates two options are available: it can be defined in the relative frame of reference or in the absolute frame of reference. e.8) Grid positioning for a slot The user specifies the width of the slot. The width of the slot is used to calculate the outgoing velocity. From the grid indices a geometrical point is defined. Then the slot is defined in the same way as for the Cylindrical positioning (section e.9). 8-46 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models FIGURE 8.6.2-35 Geometry Parameters for Grid positioning of a slot Finally, three ways to impose the injection direction are proposed through the interface: Cartesian, cylindrical or grid indices. When Grid Indices is selected, refer to the end of section e.1) for more details. For injection direction specified in Cylindrical coordinates two options are available: it can be defined in the relative frame of reference or in the absolute frame of reference. e.9) Cylindrical positioning for a slot The user has to specify the width of the slot. The width of the slot is used to calculate the outgoing velocity. The multi-patch selection has been restricted to the slots defined by Cartesian or cylindrical coordinates. FIGURE 8.6.2-36 Geometry parameters for space Cylindrical positioning of a slot For the positioning of the slot, the radius and z values are asked to the user. The closest cell face of the patch to this point is found. The radius and axial position of this cell face centre becomes the slot position in the (r,z) plane. It should be noted that this slot position is not identical to the initial user input. For most axial machines the radius can be easily identified by calculating the closest point on the patch. In this case only the axial position of the slot is required in the interface. For radial machines, or for axial machines with complex vein geometry, the two components of the original point are required (Figure 8.6.2-37). FINE™/Turbo 8-47 Dedicated Turbomachinery Models Cooling/Bleed Axial Machine Radial Machine FIGURE 8.6.2-37 Examples of slot positioning The algorithm that defines the cell faces that are concerned by this slot is illustrated in Figure 8.6.238. For each cell face of the patch, the two extremities in the (r,z) plane of this polygon (A,B and A’,B’) are identified (i.e., the two vertices with the maximum distance in this plane). They define the limits of the cell face in the (r,z) plane. If those two points are called A,B for cell 1 and A’,B’ for cell 2, and S is the slot location specified by the user in the (r,z) plane through FINE™/Turbo, as presented on Figure 8.6.2-38, S is only included in the domain of cell 1 limited by A,B in the (r,z) plane, therefore, the cell 1 is the only cell concerned by the slot S. FIGURE 8.6.2-38 Identification of the cells concerned by the slot S in the (r,z) plane. δ is the distance between A and B. On the contrary, S is not inside the domain defined by A',B'. Thus, the cell 2 will not be concerned by the slot. For O-meshes with small cells close to leading or trailing edges, this algorithm could leads to missing cells. This problem is due to a (r,z) position specified by the user in 8-48 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models FINE™/Turbo for the slot that is not precise enough. not precise enough value exact value points are missing FIGURE 8.6.2-39 Definition points are represented of a slot for a O-mesh Furthermore, in order to ease the capture of the right coordinates, the button Get Coordinates enables the user to interactively select the point in the mesh view after opening the mesh through the menu Mesh/View On/Off or Mesh/Tearoff graphics (only available on UNIX). Finally, three ways to impose the injection direction are proposed through the interface: Cartesian, cylindrical or grid indices. When Grid Indices is selected, refer to the end of section e.1) for more details. For injection direction specified in Cylindrical coordinates two options are available: it can be defined in the relative frame of reference or in the absolute frame of reference. f) Flow Parameters The user may specify the Mass flow or Mass flow relative to inlet. The specified mass flow is actually the total mass flow through all the blades and through all the holes in the case of a line of holes. Thus the mass flow through one hole is the specified mass flow divided by the number of blades and the number of holes. The mass flow is often responsible for initialization troubles as it might be too high. The FINE™/Turbo interface allows a tuning of the specified mass flow through an expert parameter. This is described in section 8-6.3. For cooling flow the mass flow specified in FINE™/Turbo will be considered as positive. The mass flow is considered as negative for bleed flow. When Mass flow relative to inlet is selected, a new pop-down menu appears. The user has to choose an inlet patch (or group). The cooling/bleed mass flow is specified as a percentage value of the inlet mass flow. In case the user changes the inlet grouping in the Boundary Conditions page, a warnFINE™/Turbo 8-49 Dedicated Turbomachinery Models Cooling/Bleed ing box will appear if the patch/group that links to the injectors is changed. It is strongly advised to verify the patches in the injectors definitions after performing inlet group/ ungroup in the Boundary Conditions page. Since the injected flow is relative to an inlet mass flow, the injected flow can strongly varies with iterations when Mass flow relative to inlet is selected. This can lead to unstable behaviour if the injected flow is important with respect to the inlet mass flow. In that case it should be recommended to start from a previously converged solution. FIGURE 8.6.2-40 Flow FIGURE 8.6.2-41 Flow parameters for Bleed parameters for Cooling Furthermore, the Arrows scaling factor parameter enables the user to control the shape of the arrows representing the injection direction after opening the mesh through the menu Mesh/View On/Off or Mesh/Tearoff graphics (only available on UNIX). For cooling additional parameters have to be defined: • static or total temperature in absolute or relative frame of reference. • turbulent kinetic energy and dissipation or turbulent intensity for the k-ε model. 8-50 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models • kinematic turbulent viscosity for the Spalart-Allmaras model. The detail of mass flow through each injector and the maximum Mach number in the injector has been added in the .mf file. The user can verify whether his/her data is acceptable. 8-6.2.2 Preview/Preview&Check Injector Sector When adding an injection sector into FINE™/Turbo, the location (cell face are highlighted) and the direction of the injection can be visualized. In order to be able to visualize, the user has to load the mesh through the menu Mesh/View On/Off or Mesh/Tearoff graphics (only available on UNIX). Switch off Spreading of the holes FIGURE 8.6.2-42 Injection Switch on Spreading of the holes sector visualization within FINE™/Turbo The parameters area will then be overlapped by the graphic window, and the small control button on the upper - left corner of the graphic window can be used to resize the graphics area in order to visualize simultaneously the parameters and the mesh (see Chapter 2-6.6). Select the injectors and Click-left on the Preview button, a vector will be shown at each hole center if a line or a single hole is selected. If a slot is selected, the vectors are shown at the center line of the slot and there is a vector for each cell crossed by that line. When the Spreading of the holes is switched on, the color contour of the surface fraction is represented on the mesh of the wall (see section FIGURE 8.6.2-42). This quantity corresponds to the surface fraction of each cell that is "touched" by a hole.The color contour varies from blue to red as the fraction goes from 0 to 1. But if holes are overlapping in a cell, causing the cell fraction to exceed 1, the cell will be displayed in white. If the injection direction is imposed in cylindrical, whatever the reference frame selected (absolute or relative), the arrows representing the injection direction is displayed as for the cylindrical relative frame of reference. When a Points type of holes is selected, the button Preview will be changed to Preview&check. After the mesh is loaded, the holes location can be visualized and checked by pressing Pre- FINE™/Turbo 8-51 Dedicated Turbomachinery Models Cooling/Bleed view&check. The selected holes in the list are highlighted. If a hole location is wrong, the GUI prompts the user to remove it. If not, the wrong one is tagged as invalid in the list and displayed in red. Furthermore, new outputs have been added into FINE™/Turbo on the Outputs/Computed Variables page under the tab Solid data in order to enable the visualisation in CFView™ of the injected flow (in [kg/s]) and the injection direction (normalized [0 1]). The scale of the Injection Direction vector is normalised by the ratio of the surface of the injector relative to the cell surface. For example, 1 means that the cell is entirely covered by the injector and 0 means that there is no injector in this cell. . FIGURE 8.6.2-43 Injector sector outputs for CFView™ Within CFView™, the injection direction is always visualized in a relative frame of reference. 8-6.2.3 Multiple edit and copy of the injectors By selecting many injectors, the user can modify their parameters at the same time. The user can also copy injectors from one blade to another blade and use the Repetition display of the mesh in order to verify the continuity of injectors lines. a) Multiple select and edit In the case of multiple selection, the buttons Add injector, Edit injector and Remove injector change their names to Duplicate injectors, Edit injectors and Remove injectors (a). The information area in the lower part of the page (b) displays the number and the sum of cooling and bleed mass flow of selected injectors. Clicking with the right mouse button on the selected injectors will display a popup menu as shown in section FIGURE 8.6.2-44 (c), which enables to add/edit/remove the injectors or select all injectors through the position or role of the injectors. Loading the mesh through the menu Mesh/View On/Off or Mesh/Tearoff graphics (only on UNIX), then selecting the injectors and Clicking-left on the Preview button will simultaneously display the selected injectors in the graphic view. 8-52 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models (C) (A) (B) FIGURE 8.6.2-44 Cooling/bleed page for multiple selection of the injectors Multiple edit can only be used to modify the physical parameters. And it is allowed only for injectors of the same type. A check is performed when the Edit injectors button is pressed and a warning is displayed in case the selection contains injectors of different parameters: Edit of multiple injectors is possible only for injectors of the same type (cooling or bleed). Confirm the warning, a Edit Multiple Injection Sectors dialog box is given as shown in section FIGURE 8.6.2-45. The users can modify the flow parameters in this dialog box. The empty entries are displayed for the quantities that have different values in the selected injectors. The empty entries and choice buttons have different background color in order to be easily noticed by users. FIGURE 8.6.2-45 Multiple FINE™/Turbo edit for selected injectors 8-53 Dedicated Turbomachinery Models Cooling/Bleed In order to see the different values in the selection for a parameter, the user has to click in the empty entry and press the line down arrow key. A list box will be displayed below the empty entry, which contains all the values of the parameter in the selectors. The user may click on one of these values and it will be shown in the entry. The button OK will store all parameters except those of the empty entries. The button Cancel closes the Edit dialog box without saving any of the values. b) Copy and Paste When multiple injectors are selected, the selected injectors can be copied from one blade to another. In order to copy injectors, the user has to select multiple injectors, then click-left on the Duplicate Injectors button. A Wizard page will be displayed first: The blades on which the selected injectors are located are highlighted with green color. The user has to specify the new blade on which the injectors will be copied and a prefix to be added to the names of the new injectors. The selected injectors will be copied to the selected blade if there are not injectors at the specified position on the chosen blade and there are not injectors with the specified new name (prefix+selected_injector_name). Copy of injectors is possible only for injector defined on Relative on Blades. 8-6.3 Expert Parameters COOLRT (real): in case some difficulties appear at the beginning of the simulation. The robustness can be improved by reducing the imposed cooling/bleed mass flow with the expert parameter COOLRT. The value of COOLRT (less than 1) corresponds to a constant factor applied to all imposed cooling/bleed mass flow during the computation. The user should make successive computations by progressively increasing this parameter (up to 1) in case of robustness problems. MAXNBS (integer):the maximum allowed number of injection sectors is controlled through the expert parameter MAXNBS (the default value is 50). If the input file contains a higher number of sectors the parameter should be modified. 8-6.4 Cooling/Bleed Data File: ’.cooling-holes’ A parser is used to find the data in this file, using keywords to locate the position of the data in the file. The advantage of this technique is that the data do not have to be positioned at a given line in the file, but only have to be followed by the appropriate keyword (the keywords can be written with capitals or not). The user specifies a series of 'injection sectors' in the file. An injection sector is either 8-54 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models — a single cooling hole — a series of distributed cooling holes along a line (all holes having the same geometrical and flow properties) — a hub or shroud slot (continuous line of holes along a constant radius and axial position line) — a points type of cooling holes Each injection sector should respectively start and end with the keywords 8-6.4.1 Injection file format This section describes the format and the keywords used to define any kinds of cooling/bleed. A easy way to have an example of the file format for a specific type of cooling/bleed is to define a cooling/bleed in FINE™/Turbo and export it into a file using the menu Export to file. a) The header The header of the file contains the injector file version to ensure future backward compatibility. The current version is 1.0. b) Multiple injector format Each file can contain multiple injector definitions. Each injector must be delimited as following: NI_BEGIN injector NI_END injector NI_BEGIN injector NI_END injector c) Injector name NAME d) Injection geometry Type Three types of injectors can be defined: point, slot and line. In addition, the line can be straight or parametric (defined in the parametric space of the mesh patch). GEOMETRY_TYPE point GEOMETRY_TYPE straight line GEOMETRY_TYPE parametric line GEOMETRY_TYPE slot GEOMETRY_TYPE points e) Injection physical Type Two types of injectors can be defined through the interface: Bleed and Cooling FINE™/Turbo 8-55 Dedicated Turbomachinery Models Cooling/Bleed PHYSICAL_TYPE Cooling PHYSICAL_TYPE Bleed f) Locations patches The cooling/bleed must currently be defined on mesh patches identified by their indices. LOCATION_PATCH_INDICES LOCATION_PATCH_INDICES where bi, fi and pi are the block, face and patch indices. If the type is points, the user needs to specify the name of the location group instead of specifying patches. The flow solver computes automatically the positioning patches. The flow solver intersects the patches definition with the axis of the hole and chooses the closest one as the positioning patch. If the loaded mesh is generated by AutoGrid5, the following keywords can be identified: LOCATION_GROUP LOCATION_GROUP
or or The and
is used for holes defined on the blades. The and
is used for holes defined on the hub. The and
is used for holes defined on the shroud. g) Location patch index The point and slot are defined with one anchor point, the line with two anchor point. The point must be defined on one of the location patch specified by its position in the list of the location patch. POSITION_PATCH_INDEX_1 h) Anchor point location The anchor point can be defined using 4 types of coordinates: • Patch coordinates: parametric normalized arc length along I and J direction of the mesh patch STREAM_SPAN_POSITION_ON_BLADE_1 s(i) s(j) 0 STREAM_SPAN_POSITION_ON_BLADE_2 s(i) s(j) 0 #for line only AXIAL_COORDINATES <0 or 1> SIDE <0 or 1> #only for old AG4 mesh • Cartesian coordinates X,Y,Z XYZ1 XYZ2 #for line only • Cylindrical Relative R, theta and Z RTHZ1 # for slot, only r and z are important RTHZ2 # for line only • Grid Coordinates: I, J indices on the mesh patch IJ1 < j1> IJ2 < j2> #for line only 8-56 FINE™/Turbo Cooling/Bleed Dedicated Turbomachinery Models i) Cooling direction (not for Bleed) The injection direction can be defined in: • Grid Angles: angles along the I, J cst lines of the mesh IJ_ANGLES #radians • Injection vector in cartesian coordinates VXYZ • Injection vector in cylindrical relative coordinates RELATIVE_VRTHZ • Injection vector in cylindrical absolute coordinates ABSOLUTE_VRTHZ j) Anchor point location and cooling direction (for points type only) For the points type of holes, the anchor point location and the injection direction have to be defined in one line in cartesian coordinates: SINGLE_HOLE k) Mass flow The mass flow can be imposed using the following modes: • Absolute value: MASS_FLOW • Percentage of the inlet mass flow: MASS_FLOW_RELATIVE_TO_INLET l) Number of holes on a line NUMBER_OF_HOLES m) Cooling/Bleed size DIAMETER #for point, line or points type only WIDTH #for slot only n) Physical Properties Temperature: RELATIVE_TEMPERATURE or STATIC_TEMPERATURE or ABSOLUTE_TEMPERATURE Turbulent data: TURBULENT_VISCOSITY #for Spalart-Allmaras model only TURBULENT_KE or TURBULENT_INTENSITY #for k-ε model FINE™/Turbo 8-57 Dedicated Turbomachinery Models 8-6.4.2 Cooling/Bleed Examples Example 1 - Bleed Flow through a Hole defined in Grid Coordinates mode Example 2 - Cooling Flow through a Line holes defined in Patch Coordinates mode Example 3 - Cooling Flow through a Slot defined in Cartesian Coordinates mode 8-58 FINE™/Turbo Rigid Motion Dedicated Turbomachinery Models Example 4 - Cooling Flow through the points type of holes 8-7 Rigid Motion The rigid motion module allows computations in a domain where the solid boundary can move. Chapter 7-3.2.1 describes the interface and use of the rigid motion module in FINE™/Turbo. The rigid motion module can be also used in turbomachinery with the rotor/stator interface. The rotor-stator can be considered only if the interface is located between two stationary solid wall so that this is not deformed. When the rotor-stator interface is directly connected to a moving surface, an “adaptative wall” can be considered between the static wall and the moving surface. If the rotating wall is connected to the static wall by a fictitious wall (simplification of geometry), this fictitious wall becomes deformable and it can be treated when it belongs to a group named “Adaptative_wall”. The main limitations on the rigid motion module with rotor/stator interfaces are as follows: • no rotor-stator interface with deformation; • no rotor-stator interface without deformation but located between moving walls; 8-8 Aeroacoustics Acoustic noise, particularly in the aeronautical field, is of increasing importance in technological development. The noise emitted by aircraft engines is mainly due to the fan. Sound waves are created by the rotor and its interactions with the rectifier. In the single-flow turbojet or low bypass ratio supersonic flight, the jet is the main sound source. Manufacturers must be able to predict the noise to design quieter engines. FINE™/Turbo has integrated an Aeroacoustics module, which allows the user to predict the acoustic response around a turbomachinery component. The method is based on the Ffowcs Williams and Hawkings (FW-H) equation and its integral solutions (Formulation 1A of Farassat), which replaces a distributed flow interacting with the surfaces by monopole, dipole, and quadrupole sources radiating in an undisturbed medium. As first step, only monopole and dipoles sources will be considered in the current solver. The acoustic signal at the observer is directly computed by evaluating the surface integrals on the specified surfaces by the user. Time-accurate solutions of the flow-field variables (CFD sources) are required to evaluate the surface integrals. Currently, the solutions are coming from the NLH computation. Before launching the FW-H solver, the user has to launch the flow solver firstly and get a converged solution. The limitations in the Aeroacoustics module are: • The flow is subsonic; FINE™/Turbo 8-59 Dedicated Turbomachinery Models Aeroacoustics • The sound is propagated into free space; • The backward interaction of the acoustic waves on the fluid is neglected; • The flow viscosity contribution to the noise is neglected. • No parallel computation ability. In the next sections, the detailed information on the Aeroacoustics module will be given: 8-8.1 Aeroacoustics in the FINE™/Turbo GUI In order to access the Aeroacoustics module, the user needs to select the button Acoustic settings in the Flow Model page, see Figure 8.8.1-46. This button is visible only in case of Harmonic project configuration. Then the Aeroacoustics page can be accessed under the Optional Models page. FIGURE 8.8.1-46 The Acoustic settings in the Flow Model page The user must activate the option Acoustic settings before launching the FINE™/ Turbo flow solver. Otherwise the FW-H solver can not be started. If a NLH computation was performed by using the FINE™/Turbo flow solver before v8.9, the user can load the project in FINE™/Turbo v8.9, activate the option Acoustic settings and restart the computation with zero iteration. Then the FW-H solver can be started. In addition, after the button Acoustic settings in the Flow Model page is activated, a tag Acoustic Source will appear on all the boundary condition pages, see Figure 8.8.1-47. This button allows the user to select any boundary as an acoustic source (see Chapter 8-8.1.1 to know what can be defined as an acoustic source). FIGURE 8.8.1-47 The 8-60 Acoustic Source option on the Boundary Conditions page FINE™/Turbo Aeroacoustics Dedicated Turbomachinery Models The GUI for the Aeroacoustics module is shown in Figure 8.8.1-48. (A) (B) (C) FIGURE 8.8.1-48 Aeroacoustics GUI The Aeroacoustics page is divided into 3 sections: 8-8.1.1 The global parameters These parameters are needed by the FW-H solver: • Far Field Density: the mean density between the source and the observer [kg/m3]. • Far Field Sound Speed: the mean sound speed between the source and the observer [m/s]. • Period: for which the acoustic response must be computed [s]. • Number of Time Steps. • Sources on: specifies the location of the acoustic source surfaces. The sources are defined as a cloud of points on a surface with some CFD fields (pressure harmonics, density harmonics, etc.). Two kinds of sources can be used: solid sources and permeable sources. In FINE™/ Turbo, the user can define the sources on: — Mesh Bcs: the boundaries of the domain that are meshed and solved by the user. All the boundaries existing in the Boundary Condition page can be selected as the acoustic source surface. FINE™/Turbo 8-61 Dedicated Turbomachinery Models Aeroacoustics — User Defined Curve: the source can be coming from an external permeable curve defined in AutoGrid5. A surface of revolution will be created by using the external permeable curve. Please refer to the AutoGrid5 manual for more information on how to create the permeable curve. — ZCst. Cut: the user may specify a constant Z value. Then a cut plane will be created on the specified Z. • Source velocity [m/s]: the constant translational velocity imposed to the sources. 8-8.1.2 The observer definition The button Add Observer can be used to create a new observer. If an observer is selected when adding a new observer, the new observer is a copy of the selected observer. The button Remove Observers is used to remove all the selected observers from the list. Once the observer has been created, the user is able to modify its name, its location and its velocity by double clicking on the observer. Please note, there should be at least one defined observer. Otherwise it is not possible to launch the FW-H solver. When multiple observers exist in the list, the user is able to impose the same velocity components to all observers at once. If selecting one observer and right-clicking on it, a menu will appear and allow the user to "Set Vx/Vy/Vz of selected to all observers". If selecting several observers and right-clicking on them, a menu will appear and allow the user to "Set Vx/Vy/Vz of first selected to all observers". The buttons Import Settings and Export Settings are used to load or save all the parameters in this page from/to a file. 8-8.1.3 Launch Solver and Post-processing When the button Start FW-H is pressed, a new task is created and launched through the task manager. This task calls the FW-H solver with the run file as input. The task manager shows the progress status of the computation. The button Stop FW-H may be used to kill the running task. After the FW-H solver has finished the task, the button Load Results can be used to read the .fwh files and updates the available groups and field lists for selection. Multiple observers and groups can be selected for visualisation. 8-8.2 Expert Parameters for Aeroacoustics In the Expert mode, the additional parameters can be specified for the acoustic source surface. when the sources on Zcst. Cut is selected, the user may select Orientation, which is used to determine the orientation of the permeable FW-H surface. The user may change the following settings for the FW-H solver: 8-62 FINE™/Turbo Laminar-Transition Model Dedicated Turbomachinery Models • Number of harmonics: Number of harmonics used in acoustic computations (e.g. if it is set to 0, the mean CFD fields are used as input to the FW-H solver). • Far Field pressure: the mean pressure between the source and the observer • Epsilon Newton-Raphson: Level of accuracy that the Newton iterative solver has to reach before stopping the iterations. This iterative solver is used to evaluate the retarded time. 8-9 Laminar-Transition Model 8-9.1 Introduction The FINE™/Turbo solver allows the user to perform a laminar-transition simulation in order to take into account the transition onset at a certain chord distance on a blade pressure and suction sides. The transition location (transition line in 3D) should be imposed either through a user input or via a separate guess. These transition terms are activated only when the transition module is used. When it is not used, the fully turbulent version of the Spalart-Allmaras and Yang-Shih k-epsilon turbulence model remains unchanged. In the next sections the following information is given on the Transition Model: • section 8-9.2 describes how to set up a project involving the Transition Model under the FINE™/Turbo user environment. • section 8-9.3 gives a summary of the available expert parameters related to the Transition model.section 8-9.2 Transition Model in the FINE™/Turbo GUI The Transition Model can be directly activated from the FINE™/Turbo GUI by opening the Transition Model page under Optional Models. The layout of the page is shown in Figure 8.9.2-49. A list of all the blades appears in the left box and the remaining area is divided into two boxes for suction and pressure side, respectively. Four choices are possible: — — — — FINE™/Turbo Fully Turbulent Fully Laminar Forced Transition Abu-Ghannam and Shaw (AGS) Model 8-63 Dedicated Turbomachinery Models FIGURE 8.9.2-49 Transition Laminar-Transition Model Model page in FINE™/Turbo Furthermore, for Forced Transition, the user has to specify the position of the transition lines on each side of each blade. It is based on the relative stream-wise position and it is defined as a line on the blade pressure and/or suction sides from hub to shroud. The user specifies two anchor points through which a straight line will be built by the solver. It should be noted that only blades are transitional while wall ends are fully turbulent. The transition model is only available for the Spalart-Allmaras, Yang-Shih k-ε, k-ω and SST models using AutoGrid™ mesh. Rotor/Stator interfaces should be correctly oriented (from upstream to downstream) and solid walls of the blades should be adiabatic. For the Abu-Ghannam and Shaw model: only one upstream R/S interface of each blade is allowed. Furthermore, there are no restrictions on the number of inlets. For example, the transition model will not work for the Blade3 if positioning the R/S interface to the location indicated by the red lines, as shown in Figure 8.9.2-50. FIGURE 8.9.2-50 Only one upstream R/S interface directly linked to the blade is allowed The transition location imposed by the user through the Forced Transition option and by the AGS Model is only appearing if it has been defined in a turbulent boundary layer. The AGS model only works for transition from laminar to turbulent boundary layers 8-64 FINE™/Turbo Laminar-Transition Model Dedicated Turbomachinery Models but not to detached turbulent boundary layers. When detached flow is present, you’ll need to use a forced transition at a certain location. The intermittency is available on the Outputs/Computed Variables page under the tab Solid data to visualize the intermittency on solid patches in CFView™. 8-9.3 Expert Parameters INITRA (integer): control the number of multigrid iterations (default = 100) performed in fully turbulent after the coarse grid initialization process. Thereafter, the blade pressure side and suction side are identified and the transition line is defined. The computation pursue for the remaining iterations in transitional mode. The transition line derived from the Abu-Ghannam and Shaw model is computed at each iteration. Fully Turbulent MultiGrid Initialization Full MultiGrid INITRA Coarse Grid Initialization Transition Model MultiGrid For starting or restarting a computation in transitional mode from a previous solution (fully turbulent or in transitional mode) the expert parameter INITRA should be set to 0 (otherwise iterations will be performed in fully turbulent mode). INTERI (integer): control the type of intermittency distribution (0:binary or 1: from Dhawan and Narasimah) (default = 0). INTERL (integer): control the type of location used for forced transition (0: base on arc length or 1: based on axial chord) (default = 0). FTURBT (real): control the proportion close to the trailing edge that is fully turbulent (default = 0.95). FTRAST (real): prevents the transition to start in an area defined from the leading edge of the mesh. The value set is a percentage of the chord upstream of which the transition is not allowed (by default 0.05: 5%). KETRAN (Integer):control the terms multiplied by intermittency in the equations of turbulence model (default=1) 1: transition is activated for production of k 2: transition is activated for production and dissipation of k FINE™/Turbo 8-65 Dedicated Turbomachinery Models Performance Curve 3: transition is activated for production of k and epsilon BLFACT (real): factor multiplying boundary layer momentum thickness to define distance from the blade on which the transition model is applied (default=5). ITRWKI (integer):switches on the wake induced transition model. When activated (ITRWKI set to 1), the free stream turbulence intensity (defined at the inlet or at the rotor/stator interface) and the turbulence intensity from the boundary layer edge are used to define the transition region. When this parameter is not checked, only the free stream turbulence intensity is used. 8-10 Performance Curve 8-10.1 Introduction Performance curve is a graphical representation showing the characteristics of a rotating turbomachinary at various operating conditions. For example, the performance curve for a compressor would include rotor speed for various inlet and outlet pressures versus gas flow rate adjusted for temperature, density, viscosity, head, and other factors. The FINE™/Turbo environment provides a dedicated module to create and manage the performance curve computation in an automatic way. The user imposes the number of the operating points and the boundary condition. FINE™/Turbo will automatically set-up the computations of the operating points and give the performance curve. The next sections will describe the way to set-up and manage the performance curve computation in more detail. 8-10.2 Performance Curve in the FINE™/Turbo GUI 8-10.2.1 Create and Edit Performance Curve Before creating a performance curve computation, the user has to create a starting point computation, such as an operating point at design condition. Then the user needs to set the parameters and launch the flow solver until obtaining a converged solution. This starting point computation will be used as the design point to create and set the performance curve computation. To create a performance curve computation, first select the starting point computation, then click on the button Create Performance Curve on the Computations subpanel. A performance curve definition window will appear, see Figure 8.10.2-51. Here several parameters need to be inputted: • Rotation Speed: impose the rotation speed for the rotating part in the project. 8-66 FINE™/Turbo Performance Curve Dedicated Turbomachinery Models • Number of points in stall region: impose the number of the operating points in stall region. • Number of points in choke region: impose the number of the operating points in choke region. • Stall area control: select the type of the outlet boundary condition. The user can specify the outlet boundary condition with only pressure imposed in both stall and choke regions, or combining mass flow imposed in stall region and pressure imposed in choke region. • Pressure/Mass flow range in stall region: specify the varying range (%) of the pressure/mass flow rate at outlet in stall region. • pressure range in choke region: specify the varying range (%) of the pressure at outlet in choke region. • Initial Solution from: by default, the initial solution will be set as a restart from the previous operating point, except for the design point. FIGURE 8.10.2-51 Create a performance curve After clicking on the button Create, multiple sub-computations will be automatically created with the parameters that the user inputs. The present implementation is dedicated to compressor. After its creation, the performance curve may be edited to change the number of points and / or the mass flow or pressure range. To edit a performance curve, just select the name of the performance curve and click on the button Edit Performance Curve. The parameters of each of the automatically generated sub-computations may be separately modified. The flow solver may be separately started for each sub-computation. As usual, the sub-computation can be operated through the button New Computation, Rename and Remove. When a performance curve item is selected in the computations browser, the action will be FINE™/Turbo 8-67 Dedicated Turbomachinery Models Performance Curve applied to all of the subcomputations. The user may change some parameters simultaneously for all computations. 8-10.2.2 Launch the flow Solver The performance curve computation can be launched in serial model or in parallel mode. When selecting a performance curve item and clicking on the button Start Flow Solver, a window will appear, see Figure 8.10.2-52. FIGURE 8.10.2-52 Launch the flow solver for performance curve computation Selecting Start Flow Solver will launch all the sub-computations in serial mode. Selecting Perfo Curve Parallel Settings, FINE™/Turbo will automatically switch to TaskManager module and create a new task with many subtasks for all the sub-computations. A Parallel settings window will appear. The user can set the number of process and other parallel settings, which is applied to all subtasks. If a performance curve has been started and afterwards killed or suspended, the user may choose Continue from the Solver menu in order to continue computations from the first not finished subcomputation. The Continue option may also be used in case that the user adds new sub-computations to the existing performance curve in order to compute only the new sub-computations. 8-10.2.3 Output The performance curve outputs are available in a separate page, see Figure 8.10.2-53. Both pressure ratio and efficiency can be plotted. The user can also input the experimental data for comparison or export the results. If select Export to file, a data file with the name _pressureratio_efficiency.dat will be automatically created in the project folder. The option User Axis Limit can be used to specify the range of the abscissa and ordinate. The file format used to imput the experimental data is: • Line 1: Three strings defining the name of the variables. • The next lines contain the variable values of each point. Example 1: Mass Flow Pressure Ratio Efficiency 10.3443179130554 1.30143475532532 0.839340686798096 10.5739312171936 1.29300808906555 0.844243705272675 10.8034386634827 1.28314805030823 0.847144782543182 11.0327978134155 1.27196598052979 0.848022699356079 11.2620959281921 1.25955402851105 0.846824049949646 ...... 8-68 FINE™/Turbo SubProject Management Dedicated Turbomachinery Models FIGURE 8.10.2-53 Performance curve output 8-11 SubProject Management 8-11.1 Introduction The FINE™/Turbo environment allows the partial treatment of multistage turbomachinery projects. Turbomachinery applications can be naturally decomposed into several domains, e.g. rotor, stator... This natural decomposition can also be performed in FINE™/Turbo, by means of a so-called SubProject. After performing a first computation on the full turbomachine (Main Project), the user can create SubProjects, containing only part of the machine. This allows a fast and easy optimization of the geometry of each row. Afterwards, the results obtained on part of the machine can be merged together again with the full turbomachine. The access to the SubProject module requires a special license feature. Please contact our local sales or support office for more information about how to obtain a license. The next sections will describe the way to set-up and control the SubProjects in more detail. FINE™/Turbo 8-69 Dedicated Turbomachinery Models SubProject Management 8-11.2 Set-up of SubProjects in FINE™/Turbo 8-11.2.1 Grid Requirements The SubProject module is available for projects of which the mesh has been created with IGG™ or AutoGrid™. Following requirements have to be respected when generating the mesh: • Butterfly blocks in IGG™ is not compatible with sub-project management. • All rotor-stator interfaces have to be defined in the absolute way. This can be defined in the rotor-stator properties dialog box in AutoGrid™. • The final mesh has to be saved in the _mesh directory of the main project. 8-11.2.2 Create SubProjects Once the mesh of the main project has been created, the main project has to be set-up in the FINE™/Turbo GUI. After creating the project and when the mesh is loaded for the first time, the user has to activate Use Grid Configuration in the Grid Units and Project Configuration dialog box, see Figure 8.11.2-54. When the mesh is loaded, the Grid Configuration subpad will appear in the interface, see Figure 8.11.2-55. FIGURE 8.11.2-54 Use Grid Configuration Left-Click FIGURE 8.11.2-55 8-70 Grid Configuration Subpad in the FINE™/Turbo GUI FINE™/Turbo SubProject Management Dedicated Turbomachinery Models Before creating a SubProject, the main project has to be executed first. The final solution of the main project will be used as the initial solution for the SubProjects. Therefore the main project should be run until satisfactory convergence is reached. In the main project, all rotor-stator interfaces have to be defined as Full Non Matching Mixing Plane. The type of several rotor-stator interfaces can be changed simultaneously by selecting one rotor-stator interface, hold the button and left-click on the desired type of rotor-stator interface, see Figure 8.11.2-56. All settings, such as the ID Number, will be kept. - Left-Click FIGURE 8.11.2-56 Rotor-Stator Interface Settings After completion of the main project, a SubProject can be created in the following way: • Go to the Grid Configuration subpad. • Right-click on Main Project and select Duplicate. A new SubProject is created. Right-Click FIGURE 8.11.2-57 Create SubProject • By left-clicking and holding the button, several rows of the newly created SubProject can be selected. • Right-click allows to delete the selected rows from the SubProject, see Figure 8.11.2-58. FINE™/Turbo 8-71 Dedicated Turbomachinery Models SubProject Management Right-Click FIGURE 8.11.2-58 Delete Rows from SubProject The settings for the SubProject are copied from the main project and adjusted if necessary. • Boundary Conditions: Settings for in- and outlet are automatically changed if necessary. A special boundary condition From Rotor/Stator has been created. This will transfer the quantities from the rotor-stator of the main project as in- and/or outlet condition. The From Rotor/Stator boundary condition is only available for SubProjects and is set by the FINE™/Turbo GUI automatically. These settings should not be modified by the user. • Initial Solution: The initial solution is set automatically to From File. The solution of the main project will be used as an initial solution. • Control Variables: The settings are identical to the main project. Settings that are changed manually by the user when a SubProject is selected, e.g. number of iterations, will be transferred to the main project. FIGURE 8.11.2-59 Boundary Conditions for SubProject The SubProject can be executed in the same way as the main project. The computation will continue until the maximum number of iterations is reached or the convergence criteria is satisfied. 8-72 FINE™/Turbo SubProject Management Dedicated Turbomachinery Models 8-11.2.3 Modify & Merge SubProjects The SubProject module allows the user to change the geometry of the subproject. A computation can be done on the changed geometry, before inserting it back in the main project. a) Modify Geometry The geometry can be modified in following way: • Select the SubProject which contains the row of which the geometry needs to be changed • Switch to AutoGrid™ by using the Modules menu. If the mesh of the subproject has not been created yet, a warning message will appear informing the user that the mesh of the main project will be loaded. • Before being able to modify the geometry of the SubProject, the mesh of the SubProject has to be saved separately. More information on this subject, can be found in the Grid Configuration section of the AutoGrid™ user manual. Only the geometry of the subproject can be modified. The topology of the mesh and the number of grid points have to be kept equal to the main project. • After generating and saving the mesh of the SubProject, switch back to the FINE™/Turbo GUI by using the Modules menu. AutoGrid™ automatically saves the mesh of the SubProject in a separate folder in the _mesh directory. More details can be found in section 8-11.2.4. • The mesh of the SubProject will be automatically linked to the computation. The computation of the modified SubProject can be launched in the exact same way as the main project. b) Merge SubProjects When the computation of the SubProject is finished successfully, the modified geometry can be transferred to the main project. This is done by means of a merge process. The rows of which the geometry was modified in the SubProject, will replace those rows in the main project. Following procedure has to be followed: • Select the main project from the Grid Configuration subpad and switch to AutoGrid™. • Execute the Merge process in AutoGrid™, more information can be found in the Grid Configuration section of the AutoGrid™ user manual. When the merge process is completed, switch back to the FINE™/Turbo GUI. AutoGrid™ automatically saves the mesh of the merged project in a separate folder in the _mesh directory. More details can be found in section 8-11.2.4. • The merged project is now available from the Grid Configuration subpad in FINE™/Turbo. FINE™/Turbo 8-73 Dedicated Turbomachinery Models FIGURE 8.11.2-60 SubProject Management Merged Project in Grid Configuration Subpad The merged project will behave in the same way as a SubProject. The computation settings are transferred from the main project, and adapted automatically if necessary. 8-11.2.4 File Structure The files generated by the SubProject module are stored in following way (Figure 8.11.2-61): • The mesh of the main project is stored in the _mesh directory, located in the project directory. • The computations of the main project are stored in the project directory, with name _ • The mesh of a SubProject is stored in a separate folder in the _mesh directory, with name _ • The results of the computations of a SubProject are stored separately for every SubProject in the project directory. The name of the directory is equal to . In every SubProject directory, the results of each computation are saved separately. FIGURE 8.11.2-61 8-74 SubProject File Structure FINE™/Turbo CHAPTER 9: 9-1 Initial Solution Overview FINE™/Turbo provides the possibility to start a computation from an initial solution. The following initial solution types are available: • constant values, • from file, • for turbomachinery, • from throughflow. Each of these types is described in the next sections. FINE™/Turbo allows to define a different initial solution type for each block or group of blocks. Such a block dependent initial solution provides more flexibility in the restart of previously computed solutions. The next section describes how to set up a block dependent solution. 9-2 Block Dependent Initial Solution This procedure permits to initiate the calculation of some of the blocks with the results of a previous calculation, whereas the other blocks are started from a uniform flow. Another possibility is to initiate one new calculation with the results of several previous calculations. This is for instance the case if a multistage turbomachinery calculation is preceded by the calculation of the separate stages. The flow solver can start from files resulting from calculations performed on different grid levels. Only the grid levels that are used in the multigrid cycle are considered here. For instance, a computation of a three-stage turbine can start from three solutions for each stage, each one on a different grid level. Furthermore, the full multigrid cycle is automatically removed when at least one file is provided on the finest grid level. FINE™/Turbo 9-1 Initial Solution 9-2.1 Block Dependent Initial Solution How to Define a Block Dependent Initial Solution The Initial Solution page is divided in two parts. On the left, a tree displays the structure of the groups of blocks. On the right, five ratio buttons allow the user to choose the type of initial solution: constant values, restart from a solution file, turbomachinery oriented, technological effect (AutoGrid™ effects) or restart from a throughflow file. At the bottom three buttons allow to modify the group(s). It is possible to create new groups of blocks in the same way as for the groups of patches on the boundary conditions page (see section 5-2). Different initial solutions can be assigned to these groups of blocks. The Reset Turbo Groups button allows to retrieve the default grouping proposed by AutoGrid™. Two defaults are available depending on the mesh and the application type: • The first one is dedicated to turbomachinery applications, meshed by AutoGrid™. The Turbomachinery groups are automatically detected and proposed in the interface. These groups are defined by the different rows (group named "ROWS") and the technological effects. The static pressure has to be specified at the main inlet and at the rotor-stator interfaces. If the user modifies the groups, clicking on the button Reset Turbo Groups can restore the default turbomachinery grouping. • The second default is general. All the blocks are grouped in one group named "MESH" and constant values are selected. In the constant values page, the toggle option Cylindrical is set on. FIGURE 9.2.1-1 9-2.2 Initial Solution default settings when loading AutoGrid™ mesh Examples for the use of Block Dependent Initial Solution The block dependent initial solution is helpful in many industrial cases. The following are two scenarios in which this capability is very useful: 1. 9-2 A solution has been calculated for a turbine including 10 stages. A new stage is added. Now the turbine has 11 stages. The designer does not want to begin a computation from scratch for the turbine with 11 stages. He can take advantage of the solution that has been found for the 10 first stages. The new computation will contain one group with the 10 stages and one group with the last stage. The first group will be assigned to a from file initial solution and the second group can be assigned to another type of initial solution. FINE™/Turbo Initial Solution Defined by Constant Values 2. Initial Solution A turbine includes 10 stages. Even with the turbomachinery-oriented initial solution, the code does not succeed to converge properly. The designer could split the turbine in several parts and calculate the solution for each of these parts. Then a global project is created. In the Initial Solution page, a from file initial solution is assigned to each part of the project. The computation will have a far better chance to succeed. 9-3 Initial Solution Defined by Constant Values When selecting constant values on the Initial Solutions page, the user can modify the physical values used for the initial solution on the page. The physical values are uniformly used as initial solution all over the selected group of blocks, except on the boundaries. The variables for which initial values need to be specified are the static pressure, the static temperature, the velocity components and the turbulence-based variables k and ε, if a k-ε, k-ω or v2-f turbulence model is used. Note that the velocity components specified by the user are the Cartesian (cylindrical) ones for a Cartesian (cylindrical) case. Flow Direction: the lower part of the page allows for a further control of the initial field. First, for both Cartesian and cylindrical projects, the velocity direction can be fitted along the I, J or K mesh lines. The reverse option determines whether the velocity vectors will point in the I (J or K) increasing or decreasing direction. By default, no specific velocity direction is set and the input box is set to None. Velocity Fitting: for the cylindrical projects only, an option for the fitting method can be chosen. The first option fits v m , the meridional velocity (defined as v m = 2 2 v r + v z ), and uses v θ to set the azimuthal absolute velocity. The second option fits w (default), the relative velocity, to the mesh lines. Pressure Field: for the cylindrical projects only, it is also possible to act on the initial pressure field. To this end, two options are available: constant pressure field (default) and a radial equilibrium pressure gradient. In a rotational machinery for instance, a radial equilibrium pressure gradient is often closer to the physics than a constant field. The radial equilibrium factor allows to adjust the influence of the pressure gradient (its default value is 1.0). 9-4 Initial Solution from File 9-4.1 General Restart Procedure To continue on the result of a previous computation the user must simply select the solution. Clicking on the Open Browser button will open a File Chooser window to select the ".run" (or ".cgns") file of a computation. To restart from a solution the computation definition file with extension ".run" is not sufficient. It is required that the solution file with extension ".cgns" is present, which contains all the saved and requested quantities. An initial solution from file can be used only for computations that have the same FINE™/Turbo 9-3 Initial Solution Initial Solution from File topology: same blocks and same grid points distribution. FIGURE 9.4.1-2 Restarting from a file The option Reset convergence history can be activated. When activating this option the ".res" file, which contains all the residuals from the previous computation, will be erased. The new residuals will be calculated with respect to the first iteration of the new computation. If the from file solution is already very close to the exact solution, the normalized residuals will decrease slowly, because the starting state is already a good approximation of the solution. By default, the option Reset convergence history is deactivated. In this case, the new residuals are appended to the ".res" file and are calculated with respect to the first iteration of the old computation. In order to keep the convergence history, the following limitations must be satisfied: • All the blocks in the Initial Solution page must be grouped in only one group. If several groups of blocks exist, the option is disabled and automatically the convergence history is reset. • If the ".run" and ".cgns" files (initial solution) do not belong to the active computation, the ".res" file located in the initial solution folder must be copied to the active computation folder. Otherwise, the option Reset convergence history is activated automatically. For example, perform the following steps: (1) Compute a solution; (2) Create a new computation; (3) In this new computation, select a from file initial solution and choose the computed solution in step (1). The Reset convergence history option will be activated automatically, even though the new computation will start from a previous solution. If the user wants to keep the convergence history in the new computation, the user has to copy the ".res" file from the old computation directory to the new computation directory and to rename it with the name of the new computation. • If the ".run" and ".cgns" files (initial solution) do not belong to the active computation, the ".steering" and ".steering.binary" files located in the initial solution folder should be copied to the active computation folder. Otherwise, the convergence history of the global residual before restart will be lost. Note, the user must close the FINE™/Turbo interface before copying the ".steering" and ".steering.binary" files. As the initial pressure and temperature fields are block dependent, discontinuities in these quantities can be present at block connections. The flow solver could have difficulties to converge in such a case. Therefore boundary conditions should be carefully checked in order to avoid any large discontinuities at block connections. 9-4 FINE™/Turbo Initial Solution for Turbomachinery Initial Solution The flow solver can start from files resulting from calculations performed on different grid levels. Only the grid levels that are used in the multigrid cycle are considered here. For instance, a computation of a three-stage turbine on 0/0/0 with 3 grid levels can start from three solutions for each stage, each one on a different grid level (0/0/0, 1/1/1, and 2/2/2). Furthermore, the full multigrid cycle is automatically removed by the flow solver when at least one file is provided on the finest grid level. 9-4.2 Restart in Unsteady Computations To allow a second order restart for unsteady computations, it is necessary to set in the Control Variables page Multiple Files in the Output Files. This parameter allows to have multiple output files: for each saved time step also the solution of the previous time step is saved. To perform a second order restart for an unsteady computation, select from file in the Initial Solution page. Using the File Chooser select the solution file with extension ".cgns" at a certain time step "ti" ("_ti.cgns"). The FINE™/Turbo solver will automatically find the solution of the previous time step if present ("_ti-1.cgns"). If the FINE™/Turbo solver can not find the solution of the previous time step a message will appear in the Task Manager to indicate that a first order restart will be performed. Note, in order to perform a second order restart for an unsteady computation, the option Reset convergence history MUST be deactivated. Otherwise only a first order restart will be applied automatically. Please refer to Chapter 9-4.1 on how to deactivate the option Reset convergence history. 9-4.3 Expert Parameters for an Initial Solution from File There is no current limitation to start a k-ε, k-ω or v2-f computation from a Baldwin-Lomax solution. In this case, the turbulent quantities are estimated from the friction velocity if the expert parameter INIKE is set to 2 (default value) or from the turbulent viscosity field μt if INIKE = 1. In the latter case, the turbulent viscosity is initialized or read from file depending on the value of the expert parameter IMTFIL (default value IMTFIL = 0 to initialized μt or IMTFIL = 2 to read μt from file). 9-5 Initial Solution for Turbomachinery The initial solution for turbomachinery is dedicated to the cylindrical rotating machinery. This type of initial solution respects the inlet and outlet boundary conditions and assumes a constant rothalpy along axisymmetric stream surfaces. In addition, the velocity field is automatically aligned with the blade passage. The initial solution for turbomachinery is not available when imposing supersonic inlet boundary condition. The initial solution for turbomachinery is not available for bypass configuration. In a bypass configuration, the flow solver considers the minimum outlet pressure found on the both outlets in order to set the initial solution for turbomachinery. This can lead to a bad initial solution and a crash of the flow solver in few iterations. FINE™/Turbo 9-5 Initial Solution Initial Solution for Turbomachinery 2D profiles are not supported when using the initial solution for turbomachinery. 9-5.1 Methodology The initial solution for turbomachinery is computed on the 2D meridional view divided into different parts named "meridional sectors". The control sections of the meridional mesh in AutoGrid™ that correspond to the inlets, outlets and rotor-stator interfaces define these meridional sectors as showed in Figure 9.5.1-3. FIGURE 9.5.1-3 Additional data necessary for computing initial solution The conservation of mass and rothalpy is applied on the streamlines of each meridional sector. Then the initial solution computed in the meridional view is interpolated in the 3D mesh. Such initial solution ’for turbomachinery’ can also be used for the blocks defining technological effects. For example the axisymmetric elements such as seal leakages that are not included in the general meridional view can be treated easily. If the cell centre is not located in the meridional view, the pressure will be the pressure in the closest cell of the meridional mesh (idem for the temperature). The components of the velocity will be set to zero. This special treatment can be applied as well to the blocks included in 3D effects located in the main passage (cooling holes, …). Selecting the page techno effects uses this initial solution. Modifying afterwards the AutoGrid™ mesh in IGG™ can lead to a mismanagement of the blocks grouping. If some blocks are added, they are not included in the turbomachinery group, which is detected automatically by the interface. So they will not be taken into account in the initial solution ’for turbomachinery’. If some blocks are removed or renamed, the initial solution ’for turbomachinery’ will be stopped. When using a mesh created by AutoGrid™ 4, the axisymmetric stream surfaces are defined by the grid surfaces and the initial solution is applied on each block. For this the grid topology, orientation (I,J,K) and the type of down- and upstream boundary conditions are taken into account. 9-6 FINE™/Turbo Initial Solution for Turbomachinery 9-5.2 Initial Solution Grouping & Parameters FIGURE 9.5.2-4 Example of Turbomachinery-oriented initial solution The turbomachinery-oriented page displays two major panels: one for the inlet patches and one for the Rotor/Stator interfaces (see Figure 9.5.2-4). On the left of each panel, a tree shows by default the AutoGrid™ grouping. If no patch name has been given in IGG™, the default name will be a concatenation of the name of the block, the index of the face and the index of the patch. The Inlet Patches grouping displayed in this initial solution page is identical to the grouping created under the INLET tab of the Boundary Conditions page. Similarly, the Rotor/stator Interface grouping displayed in the Initial Solution page is based on the ID given in the Rotor-Stator tab of the Rotating Machinery page. These groups of patches cannot be modified in the Initial Solution page. If these groups of patches need to be edited, the user must go back to the Boundary Conditions or Rotating Machinery pages. An input dialog box is provided per group of patches in order to select the type of static pressure specification: constant distribution or radial equilibrium. One or two input boxes are provided per group of patches in order to define the static pressure value to be used and, if radial equilibrium is chosen, the radius (in meters [m]) on which this radial equilibrium will be based. Provided that a k-ε, k-ω or v2-f turbulence model is selected, a third panel is displayed that requires the initial values for the turbulent kinetic energy ( k ) and the turbulent dissipation rate ( ε ). For advice on the initial values to choose for k and ε see section 4-2.5.4. An inlet patch has to be defined among the blocks for which a ’for turbomachinery’ initial solution has been chosen. If there is no inlet patch for the selected group of blocks, a warning message is displayed in the FINE™/Turbo interface asking the user either to edit the group or to change the type of initial solution. FINE™/Turbo 9-7 Initial Solution 9-5.3 Throughflow-oriented Initial Solution Expert Parameters Some indispensable data are not available in previous versions so that the new initial solution ’for turbomachinery’ cannot be applied directly to old projects. Consequently the previous initial solution ’for turbomachinery’ is kept and applied again if the mesh file does not contain the necessary data (meridional mesh with the location and the values of the metallic angles of the leading and trailing edges in the ".bcs" file). The methodology used for the initial solution ’for turbomachinery’ is controlled by the expert parameter INITRB. By default the value is set to 2 in order to use the method for meshes created with AutoGrid™. If FINE™/Turbo detects that a mesh created with AutoGrid™ 4 is loaded, the value is automatically set to 0. In this case the old methodology is used. 9-6 Throughflow-oriented Initial Solution This type of initial solution, of interest in turbomachinery calculations, allows to get an initial field on the basis of an axisymmetric throughflow solution. The initial solution is defined through an external file created by the user. The file contains 2D data in the format described hereafter. The solver will use this data to generate an initial throughflow-oriented solution. The solver will create a virtual mesh based on the hub and shroud definitions, forcing points on the data points. Two additional stations will be created, at the inlet and outlet, respectively. The inlet data are extrapolated from the first streamwise station while the outlet data come from the last station. It is therefore recommended that the inlet and outlet boundaries of the mesh lie outside the meridional domain covered by the throughflow data. The meridional velocity is based on the mesh direction. 9-6.1 File Format The file will include three parts, that must be separated by a blank line: • solution definition, • hub definition, • shroud definition, Once it is created, the file is selected in the FINE™/Turbo interface through a File Chooser click on the Open Browser button in the Initial Solution/from throughflow page. 9-6.1.1 Solution Definition The first part of the file contains the values of the flow variables throughout a meridional structured mesh covering the entire machine. For each node of the meridional mesh, the (R,Z) coordinates are specified together with the pressure, temperature and velocity components. An axial case is taken as an example: 9-8 FINE™/Turbo Throughflow-oriented Initial Solution Initial Solution There are 4 streamwise stations in this example (Z=-0.025, Z=0.0, Z=0.025 and Z=0.05), each with 3 points in spanwise direction (R direction). The point order in a spanwise and streamwise station goes respectively from hub to shroud and from inlet to outlet. Each data line is made of the two (R,Z) coordinates (in m), the static pressure, the static temperature , the meridional velocity and the tangential velocity. The unit for grid coordinates remain alwyas in [m], the units for the other variables are dependent on the settings in the menu File/Preferences. 9-6.1.2 Hub Definition The hub definition uses the same format as for AutoGrid™. The first line must be HUB. The second line specifies the type of coordinate (ZR or RZ) and the third line the number of hub points. The next lines correspond to the hub coordinates. Taking again the example of the case above: HUB RZ 2 0.245 -0.02 0.245 0.051 #Type of data (ZR or RZ are accessible) #Number of points on hub #Point coordinates (in m) The hub is described in increasing Z coordinate from -0.02 to 0.051. The first column contains the R coordinate for each of the two points on the hub. FINE™/Turbo 9-9 Initial Solution Throughflow-oriented Initial Solution 9-6.1.3 Shroud Definition The shroud definition is similar to the hub definition, except for the first line that will be replaced by SHROUD and the points coordinates. SHROUD RZ 2 0.3 -0.02 0.3 0.051 #Type of data (ZR or RZ are accessible) #Number of points on hub #Point coordinates (in m) Meridional Average View SHROUD BLADE 3D View 1st streamwise section 2nd streamwise section 3rd streamwise section INLET 4th streamwise section OUTLET HUB FIGURE 9.6.1-1 Throughflow-oriented 9-10 initial solution FINE™/Turbo CHAPTER 10:Output 10-1 Overview With the flow solver in the FINE™/Turbo environment the user has the possibility to specify the content of the output generated by the solver. The output does not only contain the flow variables for which the equations are solved (density, pressure, velocity components, temperature), but also other variables such as total conditions, the Mach number, customized velocity projections, etc... Furthermore CFView™ allows to calculate derived quantities, which permits to limit the memory size of the output and to avoid re-launching the flow solver in case one quantity of interest is not available. With this functionality the user can find the compromise between an acceptable memory size for the output and the ease of having all flow quantities of interest immediately available for visualization. In the next sections the way to control the output from the flow solver is described in more detail: • field quantities: calculated at all the mesh nodes (see section 10-2.1), • solid data: calculated along the solid wall boundaries (see section 10-2.1.5), • customized averaged data: — the evolution of some averaged quantities can be provided along the streamwise direction as described in section 10-2.2, — for turbomachinery applications, a pitchwise averaged output can be created for visualization as described in section 10-2.3, • global performance output (see section 10-2.6), • additional output for the ANSYS code, a widely used finite element code for structural analysis (see section 10-2.5.1). The global performance output is written in an ASCII file with the extension ".mf". All other outputs, generated by the solver, are written in one single ".cgns" file, compatible with the CFView™ visualisation software. It is also possible to request for the output to be written in Plot3D format, as described in section 10-2.7. FINE™/Turbo 10-1 Output Output in FINE™/Turbo 10-2 Output in FINE™/Turbo 10-2.1 Computed Variables Using the Outputs/Computed Variables page, the user can choose which physical variables have to be included in the output generated by the flow solver, see Figure 10.2.1-1 to Figure 10.2.1-6. All the selected variables will then be automatically available when launching CFView™ in order to visualize the results. 10-2.1.1 Thermodynamics FIGURE 10.2.1-1 Thermodynamics computed variables page (for cylindrical projects) Table 10-1 and Table 10-2 give the formulae used to calculate the thermodynamic quantities. Quantity Static temperature Cartesian and cylindrical cases Incompressible Perfect gas P stat T stat = ------------ρr gas T stat Total temperature Relative total temperature Static pressure Total pressure Relative total pressure Density 2 v k T tot = T stat + -------- + ----2c p c p r w k T tot = T stat + -------- + ----2c p c p 2 r w k T tot = T stat + -------- + ----2c p c p P stat P stat v k T tot = T stat + -------- + ----2c p c p 2 γ ---------- 2 v P tot = P stat + ρ ----- + ρk 2 T tot γ – 1 P tot = P stat ----------- T stat 2 r w P tot = P stat + ρ ------ + ρk 2 ρ TABLE 10-1 Thermodynamics 10-2 2 r γ ---------- T tot γ – 1 r P tot = P stat ----------- T stat ρ quantities generated by the FINE™/Turbo solver FINE™/Turbo Output in FINE™/Turbo Output Incompressible Cylindrical cases only Perfect gas Entropy T stat s = cp ln -------------------T stat inlet Rothalpy P stat w – ω r I = cp T stat + ----------- + ------------------------ + k ρ 2 w –ω r I = cp T stat + ------------------------ + k 2 Dynamic viscosity μ μ Thermal conductivity κ κ Heat capacity cp cp Gamma - γ ( P stat ⁄ P stat inlet ) s = c v ln ----------------------------------------γ ( ρ ⁄ ρ inlet ) 2 2 2 2 2 2 ω is the angular rotation speed and r, the distance from the rotation axis The term k only exists when the two or four equation turbulence models are applied. TABLE 10-2 Thermodynamic quantities generated by the flow solver in cylindrical cases The heat capacities cp and cv are function of the temperature for real gas, while they are constant in case of perfect gas. When real gas is used, the total pressure and total temperature are computed by the following equations: T Tt 2 v c p ( T ) dT + ----- + k = 2 T ref Pt ln ----- = p c p ( T ) dT T ref Tt cp ( T ) - dT ------------r ( T )T T Furthermore five definitions of the pressure coefficient are available for internal flow (inlet and outlet boundary conditions available): CP1, CP*1, CP2, CP*2, CP3: 2 ( P – Pt ) inlet -, — CP1 = ------------------------------2 ρ inlet U ref – Pt Pt inlet -, — CP∗ 1 = ------------------------- Pt inlet 2(P – P ) inlet -, — CP2 = ----------------------------2 ρ inlet w inlet 2 ( Pt – Pt ) inlet -, — CP∗ 2 = --------------------------------2 ρ inlet w inlet 2(P – P ) inlet -. — CP3 = ----------------------------2 ρU where Xinlet corresponds to the mean value of the variable X on the inlet, and where Uref is defined as: • ω RLEN in cylindrical cases, with RLEN, the reference length given in the Flow Model page, and ω, the rotational speed (defined block per block), FINE™/Turbo 10-3 Output Output in FINE™/Turbo • UENTR (Cartesian case) to be specified in the expert parameters list of the Control Variables page. When the reference velocity Uref is set to 0, the value of CP1 and CP3 are undefined and set to 0. Finally, when a condensable fluid is selected in the Fluid Model page, new quantities at the bottom of the page will appear. Those variables are defined using the thermodynamic tables defining the condensable fluid (see section 3-2.3.4 for more details). When the condensable fluid option is used, 6 flow variables are stored at all mesh cell centers instead of 5 for a perfect gas or liquid. These variables are the following: density, velocity compo2 v nents, static pressure and total energy ( ρE = ρ e + ----- ). The static and total enthalpy can easily be 2 derived using: • static enthalpy h = e + --p- . ρ 2 v - . • absolute total enthalpy H a = h + --- 2 2 ------ . • relative total enthalpy H r = h + w 2 The dryness fraction permits to evaluate the location of the local thermodynamic state with respect to the saturation curve. For each value of the pressure an interpolation from the saturation table ("PSA.atab") permits to determine the saturated liquid (ρl) and gas (ρv) values of the density. The dryness fraction is then computed by: ( ρ – ρ )ρ ( ρ v – ρ l )ρ l v • dryness fraction X = -----------------------. The generalised dryness fraction directly results from the above expression whereas the standard dryness fraction is bounded in the [0,1] interval. The presence of the saturation table ("PSA.atab") is required in order to calculate the dryness fraction, although this table is not required by the solver itself (unless an inlet boundary condition based on dryness fraction X is used). 10-2.1.2 Velocities FIGURE 10.2.1-2 10-4 Velocities computed variables page (for cylindrical projects) FINE™/Turbo Output in FINE™/Turbo Output The velocity quantities that can be selected are described below. Both for Cartesian and cylindrical cases: • Absolute velocities: vx , vy , v z , v , v . • Velocity projections: v i , v j , vk , vi , v j , vk , vis , vjs , v ks . · v i = ( v ⋅ S i )S i with S i , surface vector of the i surface, · v is = v i – ( v ⋅ S i )S i . • Absolute Mach Number, only for compressible fluids: γP stat - . M abs = v ⁄ ------------ ρ For cylindrical projects only: • Absolute velocities in the rotating frame: v r , vθ , v m : v r = v x cos θ + v y sin θ , v θ = v y cos θ – v x sin θ , vm = 2 2 vr + vz . • Relative velocities: wx , w y , w θ , w , w : w= v – ω × r , w θ = w y cos θ – w x sin θ . • Relative velocity projections: wi , w j , w k , wi , w j , w k , wis , w js , w ks . · w i = ( w ⋅ S i )S i with S i , surface vector of the i surface, · w is = w i – ( w ⋅ S i )S i . • Relative Mach Number: γP stat M rel = w ⁄ ------------- . ρ 10-2.1.3 Vorticities FIGURE 10.2.1-3 FINE™/Turbo Vorticities computed variables page 10-5 Output Output in FINE™/Turbo The vorticity is calculated according to the following expression: ζ= ∇ × v , where ∇ is the gradient operator. From the above expression, ζx, ζy, ζz, ζxyz, and ζ are available. 10-2.1.4 Residuals FIGURE 10.2.1-4 Residuals computed variables page The residuals are computed in FINE™/Turbo by a flux balance (the sum of the fluxes on all the faces of each cell). The absolute value |RES| resulting from the flux balance is written as output for each cell. The residuals for the following quantities can be selected: • density ρ, • energy E, • velocity component wx , • velocity component wy , • velocity component wz , • turbulent kinetic energy k, for the k-ε, k-ω and v2-f turbulence models, • turbulent energy dissipation rate ε, for the k-ε and v2-f turbulence models. 10-2.1.5 Solid Data FIGURE 10.2.1-5 Solid data computed variables page The solid wall data refer to quantities that are estimated at the solid boundaries: • static pressure at walls (see section 10-2.1.1) • static temperature at walls (see section 10-2.1.1) 10-6 FINE™/Turbo Output in FINE™/Turbo Output τ • normalized tangential component Cf = ---------------of the viscous stress at walls, where τ is the 2 ρV ⁄ 2 viscous stress, V is the reference velocity and ρ is the reference density defined in Flow Model page. -------- and for the turbulent models with extended wall • heat flux at walls in general qw = κ ⋅ DT Dn function q w = ρc p u τ T τ • relative velocity at walls (see section 10-2.1.2) • viscous stress τxyz at walls yu ν • y+ (in first inner cell): y+ = -------τ- , where y is the normal distance from the walls to the first inner cell center and u τ is the wall friction velocity. • heat transfer coefficient: qw h = ------------------------------------ , ( T wall – T bulk ) in which q w is the local heat flux, T wall the local temperature at the wall and T bulk the reference temperature for convection. T bulk is controlled by the expert parameter HTCDEF (available in the expert parameters list of the Control Variables page). When setting HTCDEF to 1 (default), T bulk is equal to the absolute averaged total temperature at the inlet. When setting HTCDEF to 2, T bulk is equal to the reference temperature defined in the Configuration / Flow Model page. • Injection flow (see Chapter 8-6.2.2) • Injection direction (see Chapter 8-6.2.2) 10-2.1.6 Turbulence FIGURE 10.2.1-6 Turbulence computed variables page. The following quantities can be stored: • y+ (3D field) ρy wall u w y + = ---------------------- , μ • wall distance (i.e. closest distance to the wall: ywall), • turbulent viscosity (μt/μ), • production of kinetic energy (Production), • turbulent kinetic energy k, for the k-ε, k-ω and v2-f turbulence models, FINE™/Turbo 10-7 Output Output in FINE™/Turbo • turbulent energy dissipation rate ε, for the k-ε and v2-f turbulence models, • specific dissipation ω, for the k-ω turbulence models. 10-2.1.7 Harmonic For the output specific for harmonic computations see section 8-4.2. 10-2.1.8 Deformation FIGURE 10.2.1-7 Deformation computed variables page These output variables are only accessed when the mechanical coupling module is activated. The scalar variables Dx, Dy and Dz is the mesh deformation in X, Y and Z direction, respectively. The variable Dxyz is the mesh deformation vector. Mesh deformation output is not available when the mesh deformation is calculated in the cylindrical coordinates (IMVCYL=1). 10-2.2 Surface Averaged Variables This option is customised for turbomachinery applications and displays in a Cartesian plot the evolution of surface-averaged variables along the streamwise direction. The user has to select the blocks along the streamwise direction. A surface averaging is performed on the grid surfaces perpendicular to the streamwise direction. The plot is created by a computation on each block. The Surface Averaged Variables page is modified according to the type of project as defined in the Mesh/Properties... menu. For a Cylindrical project the page is shown in Figure 10.2.2-8. In this case the streamwise direction (by default K) is defined on the Rotating Machinery page of the FINE™/Turbo interface. The blocks to be included in the averaging, can be selected from the list of blocks by left-clicking on them. Selected blocks appear highlighted. This selection acts as a toggle where clicking ones on a block name selects the block and clicking a second time deselects the block. To select multiple blocks it is sufficient to left-click on each of them. The variables available for averaging are listed on this page and a averaging method can be selected for each variable independently. The turbulent quantities k and ε only appear for selection if a k-ε, k-ω or v2-f turbulence model is selected. 10-8 FINE™/Turbo Output in FINE™/Turbo FIGURE 10.2.2-8 Output Surface averaged variables page for a Cylindrical project Since the integration is performed on mesh surfaces, some differences could appear. For example, if the geometry contains a splitter, two curves will be generated in the Cartesian plot. A sum of these curves has to be performed to see the evolution of the quantity in streamwise direction of one channel. Since the surface averaging is performed on grid surfaces this option is only suitable for HI-topology meshes, without a skin block. For Cartesian projects as defined in the Mesh/Properties... menu the Surface Averaged Variables page is displayed as shown in Figure 10.2.2-9. In this case the streamwise direction needs to be selected directly in this page by selecting to average on surfaces of constant index (in the example of Figure 10.2.2-9 surfaces of constant K). The blocks to include in the averaging need to be selected in the same way as for a cylindrical case as described before. Contrary to a cylindrical project, in this case no relative quantities are available. Like for a cylindrical project the surface averaged evolution of the quantities is shown for each block separately. FINE™/Turbo 10-9 Output Output in FINE™/Turbo FIGURE 10.2.2-9 Surface averaged variables page for a Cartesian projects After selecting such averaged variables, they are available through the menu Quantity/Plot Data within CFView™, which is automatically plotting the averaged variable along the selected streamwise direction on each I, J or K constant surface. 10-2.3 Azimuthal Averaged Variables The FINE™/Turbo environment provides the user with a specific turbomachinery output, i.e. the two-dimensional meridional view of the circumferentially-averaged results. Note that this functionality is also available in CFView™. Using the Azimuthal Averaged Variables page, the user can choose which physical variables have to be included in the pitchwise-averaged output generated by the flow solver. This page is therefore only accessible if the project is of the cylindrical type. The azimuthal averaging of the variables is calculated at the end of the computation. The results will be displayed as a 2D case in CFView™. The name of the file from which CFView™ can read which variables have been averaged in the azimuthal direction has the extension ".me.cfv". The choice is left to the user to apply Mass or Area averaging, and to merge the averaging patches into one patch or not. This last option (Merging of meridional patches) simplifies the meridional view but the patches are merged in increasing order one after another, which is not suitable for all mesh topologies. All the patches of the project that will be merged should be matching in spanwise direction. If Surface of revolution mesh (Autogrid) option is activated, a specific algorithm will be applied to enhance azimuthal averaging of the solution performed on revolution surfaces. The "parameters area" is divided into five ’notebook pages’ which can be selected by clicking on one of the five corresponding tabs: Thermodynamics, Velocities, Vorticities, Residuals and Turbulence in the same way as for the control variables. 10-10 FINE™/Turbo Output in FINE™/Turbo Output Figure 10.2.3-10 shows an example of the corresponding information page for thermodynamics variables. Other pages are similar to those described in section 10-2.1. At the bottom of Figure 10.2.3-10 in Expert Mode the user can define the meridional patches for azimuthal averaging. See section 10-3.1 for more detail on this possibility. By default meridional averaging patches are set. Automatic setting of the meridional averaging patches only works if no manual action has been performed (like renaming of some patches). FIGURE 10.2.3-10 The thermodynamics azimuthal averaged variables page 10-2.4 Template manager A new button “Template manager ... “ was added on the top of each of the three output pages in FINE (Computed variables, Surface averaged variables, and Azimuthal averaged variables). This button invoke a pop-up window: FINE™/Turbo 10-11 Output Output in FINE™/Turbo This new windows is the same for each of the three pages and it lets the user to Load, Save and Remove stored output selections. Double click on a profile name also loads the selected profile. The button Cancel close the window and the page will return to the its state before launching the template manager. This gives the user the possibility to browse the existing profiles without loosing his current outputs selection. To create a new outputs profile the user should click on “Save”. A new entry appears, asking for the name of the new profile: When Enter is pressed, Fine checks if the entered name already exists: The current outputs selection (the values of all check buttons in all tabs) in the current page is stored in this new profile. The button “Remove” deletes selected profile. 10-12 FINE™/Turbo Output in FINE™/Turbo Output The profiles are stored in text format in the file .numeca/fine_output.def and are independent from projects. Different users may exchange their profiles by means of this file. 10-2.5 ANSYS The FINE™/Turbo environment provides the user with a specific ANSYS output. The objective is to export results of the CFD computation on solid surfaces (nodes and elements) into ANSYS as a boundary condition for the finite element model. This approach is called FEM loading method for loading the CFD results on a Finite Element Model. The transferred results on the interface fluidstructure can be the pressure field for a structural analysis and the temperature field or the heat fluxes for a thermal analysis in the structure. The FEM approach needs to have the finite element mesh of ANSYS. If this mesh does not exist before the CFD computation, it is impossible to create directly a file that can be imported in ANSYS to apply the suitable boundary condition. Consequently the best way to manage the interface between FINE™/Turbo and ANSYS can be a new postprocessing tool. The post-processing tool is needed with the specification of the ANSYS mesh, the common surfaces where the data must be interpolated and the type of boundary condition on each surface. The transfer will be carried out through the ANSYS file saved with the command CDWRITE ("project_ANSYS.cdb") in ANSYS. This file will be modified and read again in ANSYS to impose the CFD results as boundary conditions (see Figure 11.2.4-10). FIGURE 10.2.5-11 Data transfer of CFD results into the ANSYS project 10-2.5.1 ANSYS Pre-Processing Before completing the Outputs/ANSYS pages, the user must create the file "project_ANSYS.cdb" with the command CDWRITE in ANSYS. Furthermore before the save in ANSYS, some operations are needed to allow the identification of the common surface between the fluid model and the structural model. The ANSYS project must be completely defined with a special treatment for the surface loads that will be replaced by the interpolated CFD results. On each common surface, a coded constant value is specified. The default coded values are given in the Table 10-3 for the different types of boundary condition. The value is incremented by one for each different sur- FINE™/Turbo 10-13 Output Output in FINE™/Turbo face so that for example the pressure imposed on the first surface is set to 1000001 and it is set to 1000002 on the second,... Boundary Condition Pressure field Temperature field Heat transfer coefficient Heat flux TABLE 10-3 Default Code 1000001 2000001 3000001 4000001 code for different type of boundary condition imposed from CFD results The coded value can be modified in order to avoid confusion with physical values. Note that the surface must be relatively flat or smooth (without sharp angle) so that the six surfaces define a cube. Moreover a surface closed on itself, like a cylinder or a blade must be divided into two parts if the conservative interpolation type is required. The heat transfer coefficient can be computed only for non-adiabatic solid patches. The correct physical bulk temperature must be specified on the surfaces with convection. It must be constant for each surface. If the coded values have been prescribed by using the solid model, the solid model has not to be saved in the original ".cdb" input file (see the options for achieve file). The ansys importation does not support a time profile of a quantity. Validation tests are performed with ANSYS release v8.0. Please refer to ANSYS user manual for more details on the ".cdb" file format 10-2.5.2 Global Parameters The user can complete the Outputs/ANSYS pages when the file "project_ANSYS.cdb" has been created (refer to section 11-2.4.1 for more details). Firstly, the user needs to specify under the tab Global Parameters in Boundary Conditions (Figure 10.2.5-12 - (1)) the coded constant value used in the file "project_ANSYS.cdb". The default coded values are given in the Table 10-3 for the different types of boundary condition. Furthermore, the user has to specify the required units of the data for each type of boundary condition. The units will be specified next to the coded value. Then, the user needs to load the file "project_ANSYS.cdb" (Figure 10.2.5-12 - (2)) created in ANSYS (refer to section 10-2.5.1 for more details) in Input File. The data transfer between the CFD mesh and the structural mesh is possible if the common geometries are matching. It is possible that this condition is not fulfilled and the causes can be diverse: • Units: a first difference can come from the units of the meshes. Consequently the units used in the ANSYS mesh must be specified in ANSYS Mesh Units. The conversion Factor will be deduced automatically (Figure 10.2.5-12 - (3)). • Reference system: the second cause of mismatching is the use of different coordinate systems (Figure 10.2.5-12 - (3)). For example, the original geometry can be rotated for the CFD model so that the axial direction corresponds to the Z axis. The necessary conversion of coordinates 10-14 FINE™/Turbo Output in FINE™/Turbo Output will be done through the specification of the position of the coordinate center of the ANSYS mesh in the coordinate system of the CFD mesh and the specification of the location of three common points in both meshes in Reference System. FIGURE 10.2.5-12 General Parameters of ANSYS outputs Note that these points cannot be located on a line or a plane including the zero point (not linearly dependent). The coordinates are specified in their respective units. The origin of the ANSYS mesh should be at (0,0,0). Finally in Output File, the user specifies the new output file "project_CFD.cdb" (Figure 10.2.5-12 - (4)) containing the transferred CFD results on the solid boundaries coded in ANSYS (refer to section 10-2.5.1 for more details). In order to create the new output file, the user has to complete the page under the Surface Selection tab before clicking on the Create Output File button (Figure 10.2.5-12 - (5)). 10-2.5.3 Surface Selection After completion of the page under Global Parameters tab page, the user has to complete the Surface Selection page (refer to section 10-2.5.2 for more details) before creating the ANSYS output file (Create Output File button). When the ANSYS input file is read in Input File, the common surfaces on which the data must be transferred are identified in the ANSYS mesh. The FINE™/Turbo interface lists each surface with the corresponding coded value (Figure 10.2.5-13 - (1)). FINE™/Turbo 10-15 Output Output in FINE™/Turbo When reading the ANSYS input file for the first time, automatically a new file with the extension ".ANSYSgeom" is created in the active computation directory. This file contains the geometry of the related ANSYS surfaces and allows accelerating the next operations. By clicking on Selected Surface Properties button (Figure 10.2.5-13 - (2)), a new window (Figure 10.2.5-14) allows the user to specify the solid patches from which the data will be interpolated. Following interpolation parameters can also be defined: interpolation type (Interp Type) and the allowed maximal distance (Max Dist). Two different interpolation types (Interp Type) are proposed: a conservative and a non-conservative. The suitable interpolation scheme is dependent on the type of boundary conditions. The spatial field of pressure or temperature can be interpolated from cell faces to nodes whereas a conservative transfer of the heat fluxes can be preferred. Note that in the non-conservative approach, the local normal of the fluid mesh is used for the projection of the ANSYS surface on the corresponding IGG™ solid patches. Whereas an averaged local normal of the ANSYS mesh is used for the projection in the conservative approach. If the geometry of the common surfaces does not match exactly between the IGG™ mesh and the ANSYS mesh (e.g. if the fillet is not modeled in the fluid mesh), the result depends on the way to define the surfaces in ANSYS, the selection of the IGG™ solid patches from which the interpolation is performed and the choice of the interpolation type. A slight discontinuity can appear in the interpolated field. In case the fillet is not modeled, the different ways to project the ANSYS surface on the IGG™ solid patches imply that the conservative approach can fail if the ANSYS surfaces are not approximately divided in the fillet where its normal intersects the edge separating the IGG™ solid patches (blade and hub or shroud). (1) (3) (4) (2) FIGURE 10.2.5-13 10-16 Surface Selection of ANSYS outputs FINE™/Turbo Output in FINE™/Turbo Output The CFD results are read from the ".cgns" file of the active computation. The nonconservative approach needs to save the solid data on the IGG™ solid patches. For the conservative approach, only the solid data Heat Flux is required for the computation of the heat transfer coefficient. An allowed maximal distance (Max Dist) can be used to control the interpolation process by ensuring that it is performed in the nearest element of the selected solid CFD patches. The maximum distance of the ANSYS output on the surface selection page, is always expressed in meters (independent from the mesh units or project preferences) FIGURE 10.2.5-14 Add solid patches to ANSYS surface Then, the user specifies the solid CFD patches in the list of Solid Patches by or and left-click. To add or remove solid patches linked to the highlighted ANSYS surface, the buttons Add Selection and Remove Selected are used respectively. When the solid patches are well selected, the window has to be closed (Close) and the patches will appear in the list Selected Solid Patches and Groups (Figure 10.2.5-13 - (3)). A visualization of the active ANSYS surface and of the selected solid patches can help the user in the selection process after opening the mesh through the menu Mesh/View On/Off or Mesh/ Tearoff graphics (only available on UNIX). Moreover, the visualization allows checking that the surfaces (ANSYS and IGG™ solid patches) are matching. A modification of the ANSYS mesh unit or reference system is directly taken into account in the visualization when the user refreshes the view by clicking again on any ANSYS surface. To ensure a complete data transfer, the selected IGG™ solid patches have to completely overlap the ANSYS surface. The area of the selected IGG™ solid patches can be larger than the area of the ANSYS surface. Since the IGG™ solid patches defining a periodic structure can be divided (Figure 10.2.5-15), a periodic shift can be required to match the common ANSYS surface. This shift must be specified for each solid patch, highlighted in Selected Solid Patches and Groups list, in Periodicity by activating Rotation and Translation (Figure 10.2.5-13 - (4)). The rotation and translation shifts are respectively specified in degrees and IGG™ mesh units. FINE™/Turbo 10-17 Output Output in FINE™/Turbo FIGURE 10.2.5-15 Mesh differences IGG™ vs. ANSYS Moreover one ANSYS surface can be covered by a group of solid patches and by the same group which is rotated (or translated). Consequently, a duplication of the periodic solid patches is possible by activating Duplicate patch(es) after applying a Rotation and Translation to the highlighted solid patch (Figure 10.2.5-13 - (4)). FIGURE 10.2.5-16 Duplicate Option Utility Finally, the new output file can be created by clicking on the Create Output File button (Figure 10.2.5-12 - (5)). 10-18 FINE™/Turbo Output in FINE™/Turbo Output 10-2.5.4 Import Results in ANSYS The new output file "project_CFD.cdb" (Figure 10.2.5-12 - (4)) containing the transferred CFD results on the solid boundaries coded in ANSYS is now available. When reading this file in ANSYS with the command CDREAD, following rules need to be respected: • Only the FE model (file ".cdb") has to be imported. • If the coded values have been prescribed by using the solid model, the solid model has not to be saved in the original ".cdb" input file (see the options for achieve file). If the solid model is saved, conflicting values are set on the fluid-structure boundaries and the initial coded values will be kept. Moreover these artificial boundary conditions have to be removed in the ANSYS project before importing the modified archive file with the suitable boundary conditions. If they are not removed, the coded values will replace the transferred values. 10-2.6 Global Performance Output The main results for global performance are summed up in a file with extension ".mf". Inlet and outlet averaged quantities, pressure ratios and efficiency are computed and stored in this file. The ".mf" file also provides global averages at each rotor/stator interface. When there are multiple inlets or outlets with different periodicities, only one "number of blades" is reported in the .mf file, but there will be a minus (-) sign before that number to indicate that there are also other inlets or outlets with different periodicities than reported. All the variables in .mf file are mass averaged, except that the static pressure is area averaged. If the project does not involve any of inlet/outlet or interfaces (e.g. for external flow), the ".mf" file is empty. The user can select which and what kind of information is stored using expert parameters as described in section 10-3.2. 10-2.6.1 Flow Angle The relative and absolute flow angles are derived from the averaged velocity components: v α = arc tan -----θ v m wθ β = arc tan ------ vm cylindrical (10-1) v α = arc tan ----y v x wy β = arc tan ------ w x Cartesian (10-2) 10-2.6.2 Global Performance Global performance data, available in the ".mf" file, are calculated using the results at the inlet and outlet boundaries of the computational domain (index 1 and 2 refer to the inlet and outlet sections respectively). A row-by-row and/or stage-by-stage analysis can be performed by using the expert parameter RBRSBS. The additional performances stored in the ".mf" file are: the mass flow in and out, the static and total pressure ratio, the static and total temperature ratio and the isentropic and polytropic efficiency (see section 10-3.2). a) Global Performance Output for Incompressible Fluid The outputted global performance is depending on the type of the fluid. In case of incompressible fluid, the following data will be written: FINE™/Turbo 10-19 Output Output in FINE™/Turbo • Static pressure rise: p2 – p 1 • Absolute total pressure rise: pt2 –p t1 • Static Head: ( p 2 – p1 ) ⁄ ρg • Absolute total Head: ( p t2 – p t1 ) ⁄ ρg • Static temperature rise: T 2 – T 1 • Absolute total temperature rise: T t2 –T t1 • Efficiency For turbomachinery cases with a rotor, the expressions proposed in Table 10-4 are used. Several efficiency definitions are available, selected through the expert parameter EFFDEF (default: 1). EFFDEF Pumps p t2 >p t1 1 Δp t m· η = -----------------------------ρω ⋅ Torque ρω ⋅ Torque η = -----------------------------Δp m· 2 Δpm· η = ------------------------------ρω ⋅ Torque ρω ⋅ Torque η = -----------------------------Δpm· 3 Δp t η = ----------------------ρωΔ ( rv θ ) ρωΔ ( rv θ ) η = ----------------------Δp t 4 Δp t η = ---------------ρc p ΔT t ρc p ΔT t η = ---------------Δp t TABLE 10-4 Efficiency Turbines p t2 p t1 1 γ–1 ----------- η is 2 γ p-----t2- –1 p t1 = ----------------------------T t2 ------- – 1 T t1 η pol η is 3 η pol η is TABLE 10-5 Isentropic η pol T t2 ln ------- c T t1 = ----p ⋅ ----------------R p t2 ln ----- p t1 T t2 p 1 – -----ln ------2 T t1 p t1 η = ----------------------------R γ – 1= ---- ⋅ ------------------ is ---------cp T t2 p2 γ ln -----1 – ----- T t1 p η pol T t2 ln ----- T t1 cp = ---- ⋅ -----------------R p ln ------2 p t1 η pol T2 ln ----- T 1 cp = ---- ⋅ ----------------R p2 ln ----- p 1 t1 γ–1 ----------γ p----2- –1 p 1 --------------------------= T2 ----- – 1 T1 T t2 p t2 1 – ------ln ------ T t1 p t1 η = ----------------------------R - is γ–1 = ---- ⋅ --------------------------cp T t2 γ p t2 ln ------1 – ----- T t1 p t1 γ–1 ----------γ p2 ----–1 p t1 = ----------------------------T t2 ------- – 1 T t1 Turbines p t2
p t1 is h t, 02 – h t, 01 η is = -------------------------h t, 02 – h t, 01 TABLE 10-6 Isentropic 2is 1 r----dP . P0 0 Turbines p t2
and pvmd.
from the directory defined by the PVM_TMP (by default C:\tmp). 11-2.2 Multiple FINE™/Turbo Sessions During a FINE™/Turbo session all the tasks defined by the user are stored in the tasks file in the NUMECA tmp directory. This is the .numeca/tmp directory in the home directory of the user. On UNIX the home directory corresponds to the HOME environment variable. This is also true on Windows if this variable is defined and, if it is not the case, it is set to the concatenation of HOMEDRIVE and HOMEPATH environment variables. When FINE™/Turbo is started more than once at the same time, a warning indicates to the user that FINE™/Turbo is already running and can enter in conflicts with the other FINE™/Turbo sessions. The user can define tasks in both interfaces but the task definitions saved when exiting FINE™/ Turbo will be overwritten by the other sessions. Therefore, it is not advised to open multiple FINE™/Turbo sessions when the Task Manager is used. 11-2.3 Machine Connections The Task Manager allows the user to control processes on all the machines connected to the network. The rsh command is used by the PVM library to access the machines. Before using the Task Manager, the following actions must be done: 11-2 1. On Windows platforms the Numeca RSH Daemon has to be started. The user is referred to the installation note for more details. 2. Modify the .rhosts file in the home directory (on UNIX) or the rhosts.txt file in C:\WINDOWS (on Windows) in all the machines which can be used by the Task Manager. i.e.: if the machines machine1 and machine2 will be used by the users tasks from machine_master, the file in machine1 and machine2 must be modified as follows: line1: machine_master FINE™/Turbo Getting Started Task Manager where machine_master is the host name. login1 is optional. If the login on machine_master is different from login1, the user in machine_master will be asked to supply a password when connecting to machine1 and machine2. The rhosts file needs to be ended by a blank line. The file permission must be set to ’rw’ (on UNIX: chmod 600 ~/.rhosts). 3. Test the rsh command on the desired machine: an external check that the .rhosts file is set correctly is to enter the following command line: % rsh remote_host ls when the remote host is UNIX or rsh remote_host dir when the remote host is on Windows. where remote_host is the name of the machine to connect to. If the login on the remote host is not the same, ensure that the .rhosts file contains the line: remote_host local_login and in this case the command line is: % rsh remote_host -l local_login ls when the remote host is UNIX or rsh remote_host -l local_login dir when the remote host is on Windows. If the rhosts file is set up correctly, a listing of the files is shown on the remote host. On Windows, the rsh.exe executable is located in /fine#/bin/ The ssh command can be used instead of the rsh command on UNIX. To use this command, the user has to define an environment variable NI_RSHCMD in the shell before starting FINE by typing the following: •for csh or tcsh: setenv NI_RSHCMD ssh •for bash or ksh: export NI_RSHCMD = ssh Of course the settings of the NI_RSHCMD can be added to the ".cshrc", ".tcshrc", ".bashrc" or ".profile" file of the user. Due to a limitation of the PVM library, FINE™/Turbo can not be connected to a machine where FINE™/Turbo has already been started. When PVM tries to establish the connection, it detects that a server FINE™/Turbo is already running and/or pvm daemons are still running and finally refuses the connection with a warning. To solve this problem, the PVM daemons must be stopped on the machine on which FINE™/Turbo must be connected: 1. Log on the machine where the connection must be established. 2. Start FINE™/Turbo and open the Task Manager through Modules/Task Manager and use the button Shutdown of the page Hosts definition. The button Shutdown can be used to switch off all the PVM daemons of all the machines connected to FINE™/Turbo. This action will stop all the daemons on all the machines connected, kill all the tasks and finally exit FINE™/Turbo. 3. On UNIX: remove all the /tmp/pvmd. and /tmp/pvml. files. On Windows these files should be removed from the directory defined by PVM_TMP (by default this directory is C:\tmp). 4. Repeat this operation for all the machines on which the problems appear. The script cleanpvmd located in /fine#/ FINE™/Turbo 11-3 Task Manager Getting Started COMMON/, provided with the NUMECA software, will automatically perform steps 2 and 3 on all machines listed in the .rhosts file. This script is only available for UNIX platforms. Performing the script cleanpvmd will kill all the PVM daemons on every computer in the .rhosts file. This means that it will also kill the running computation that are connected to these PVM daemons. 5. If PVM still has a problem to get the connection, it will print an error message either to the screen, or in the log file /tmp/pvml. (on UNIX) or in the directory defined by the environment variable PVM_TMP (by default C:\tmp) in the log file called: pvml. . Please send this log file to our local support office. All these operations apply to the users daemons and users files. Multiple users can use the Task Manager simultaneously. No interaction appears between PVM daemons and PVM log files of different users. On Windows, when the user stops the pvmd on a remote host (using Remove Host button on the Hosts definition page) and immediately tries to restart it (using the Add Host... button), a message will appear stating that it is not possible to connect. This problem does not occur in general since there is no need to remove a host and add it immediately after. When it occurs the only solution is to wait until the host is available again (after 5 to 10 minutes). More details are available in the installation note. From time to time, when a user tries to connect on a remote host, an error message can appear very briefly: "Can not connect to RSH Port!!!" This may happen on Windows connecting to a host, disconnecting, and trying to reconnect again to the same host. There is a socket release time parameter which keeps the connection for some time. 11-2.4 Remote Copy Features on UNIX/LINUX All the tasks defined by the user are associated with files used or created by the NUMECA’s software. When the files are not visible from the machine on which the task must be launched (i.e. the files are on the local disk of the host where FINE™/Turbo is running), the user can use the remote copy feature proposed in the Task Manager. All the files needed by the tasks will be transferred into a directory (specified by the user) of the remote machine and at the end all the created or modified files are transferred back to the host machine from which the task has been launched. By default, the available remote directories are "/tmp". The user can also specify any other directory, as long as it is visible from the remote host and has writing permissions. This feature uses the rcp UNIX command. Before using the remote copy feature, it is advised to first check if the rcp command works correctly between the machines: — First try the rsh command (see section 11-2.3). — Type the command: touch test;rcp -p -r test destination_machine:/tmp/test. If no error is returned by the system, the remote copy works between the local host and the destination_machine. Errors may appear if the .cshrc file contains an stty command. In order to be able to use the remote copy feature, remove all the stty commands from the .cshrc file. — If the login on the local host is different from the login on the remote host, type the command: touch test;rcp -p -r test remote_login@destination_machine:/tmp/test. 11-2.5 Remote Copy Features on Windows As files located on the local disk are not visible from a UNIX machine, this feature is proposed to be able to launch tasks on remote UNIX platforms. The principle is the same as the one described in the previous section: local files are copied in the remote directory specified by the user, then the 11-4 FINE™/Turbo The Task Manager Interface Task Manager task starts. When it terminates, all results files are transferred in the original directory. This feature uses the rcp.exe Windows command. Before using the remote copy feature, it is advised to first check if this command works properly: — First try the rsh.exe command (see section 11-2.3). — Create a file test, then type the command: rcp -b test destination_machine:/tmp/test. If no error is returned by the system, the remote copy works between the local host and the destination_machine. Errors may appear if the .cshrc file contains an stty command. In order to be able to use the remote copy feature, remove all the stty commands from the .cshrc file. — If the login on Windows is different from the login on the remote host, type the command: rcp -b test destination_machine.remote_login:/tmp/test rcp.exe is provided with FINE™/Turbo and is located in the same directory as rsh.exe. 11-3 The Task Manager Interface 11-3.1 Hosts Definition The Hosts definition page shows the host name, the operating system, the connection status and the queuing system supported by FINE™/Turbo if any. For an explanation of the virtual machine see section 11-2.1.1. If the connection is not OK, it means that the corresponding computer is not in the virtual machine anymore. This may occur for example if the computer has been rebooted. FIGURE 11.3.1-1 Hosts definition page 11-3.1.1 Add Host When the user clicks on the Add Host... button, the interface asks for a host name and a login name. The login name is optional. It is needed only if the login of the user on the local and remote host are different. When the user accepts (Accept), the host name appears in the host list, with type of operating system and its connection status. At this point, the host is in the virtual machine, and is ready to receive a task. FINE™/Turbo 11-5 Task Manager The Task Manager Interface FIGURE 11.3.1-2 Add a Host If the connection can not be established, check for more detail in section 11-2.1, section 11-2.3 and section 11-2.4. The reason that the Task Manager freezes can be because FINE™/Turbo has been launched in background using an additional & symbol behind the command line. You can unfreeze the Task Manager with the command. It is impossible to add a host on Fedora 3 and Windows Vista operating systems. 11-3.1.2 Remove Host When the user clicks on the Remove Host button, the selected host is removed from the list, and is not in the virtual machine anymore. This operation is not allowed when a task is running on the host, to be removed, or when the selected host is the local one. 11-3.1.3 Shutdown When the user clicks on the Shutdown button, all hosts in the virtual machine are removed. FINE™/ Turbo exits and the virtual machine halts. All running tasks are killed. This option is useful when the user wants to change the machine on which FINE™/Turbo is running. See section 11-2.1.1 for more detail on virtual machines and when to change this. 11-3.2 Tasks Definition A task is a collection of subtasks, where a subtask is one of the programs with its arguments (".run" file for the FINE™/Turbo and FINE™/Design3D solver, template ".trb", geometry ".geomTurbo" and mesh ".igg" files for AutoGrid™ and macro file ".py" and ".run" file for CFView™). The different subtasks of a given task can be run simultaneously if the output of one subtask is not needed by other ones (for example: several CFView™ subtasks with different macro ".py" files or several the FINE™/Turbo solver subtasks with different ".run" files started on different computer). If the output of one subtask is needed by other ones, they must be run sequentially. For example: AutoGrid™ generates the mesh that is used for starting an the FINE™/Turbo solver computation whose output is used for starting CFView™. 11-3.2.1 Task List In this section, the user can visualize the defined tasks and their status. To create a task, just click on New Task button. The defaults task name can be modified by clicking on Rename Task button. The selected task can be removed by clicking on Remove Task button. After a subtask is defined, the Save button can be used to save all necessary files to start a parallel computation in batch mode. When a queuing system is used, a set of default templates is available in order to submit the job to the queue. New templates can also be created by the user. 11-6 FINE™/Turbo The Task Manager Interface Task Manager Once a task is created and defined (see following section), it can be started or stopped just by clicking respectively on the Start or Stop button. The user can delay the start of a computation by clicking on Delay button. A dialog box will appear where the user can set a task that will be launched at the specified date and time or after another specified task has finished. The delayed task can be disabled using the button Cancel. When the user validates the data, a little watch in the task list indicates that the task is scheduled: FIGURE 11.3.2-3 Task List with Delay window to start a task at a later moment When setting a task that will be launched after another specified task has finished, the reference task should not be a computation launch from the FINE™/Turbo GUI. Otherwise the delayed task will not start. 11-3.2.2 Task Definition In this section the subtasks of the selected task are listed. A subtask is defined by its type (FINE™/ Turbo solver, AutoGrid™, CFView™ or Design3D), its status and the host on which they are launched. To add a subtask click on the New button in Task Definition area. Select the executable name (FINE™/Turbo solver, AutoGrid™, CFView™ or Design3D) and the host on which the process should be started, from the two available lists. The host name list contains the hosts that are in the virtual machine. They are set in the Host definition page. 11-3.2.3 Subtask Arguments a) Definition of Input & Output Once a subtask is created, input and/or output files must be defined in the Subtask Arguments & characteristics section: FINE™/Turbo 11-7 Task Manager The Task Manager Interface — The FINE™/Turbo solver and the FINE™/Design3D solver require one argument file: the name of the ".run" file. This files is created using the menu File/Save Run Files in the FINE™/Turbo GUI and FINE™/Design3D GUI. — The mesh generation system AutoGrid™ requires three files as arguments: the ".trb" file, the ".geomTurbo" file and as output the grid file ".igg" (see the AutoGrid™ User Manual for more details) When working on a remote host, the process still requires a valid display. On Windows platforms, it is not possible to transfer the display, therefore the mesh generation has to be executed locally. On Linux platforms, the command has to be executed on the local machine. — The flow visualization system CFView™ requires two files: the ".run" file and a macro file ".py" (see CFView™ User Manual for more details) When working on a remote host, the process still requires a valid display. On Windows platforms, it is not possible to transfer the display, therefore the flow postprocessing has to be executed locally. On Linux platforms, the command has to be executed on the local machine. The run file is automatically opened by CFView™ before starting the macro. The macro file may open other ".run" files to perform flow comparisons (see CFView™ User Manual for more information about the macro ".py" file). 11-8 FINE™/Turbo The Task Manager Interface Task Manager b) Simultaneous or Sequential Mode Moreover, a process can be executed simultaneously with the other subtasks (by selecting Run Simultaneously with Previous Subtask) or sequentially (by selecting Run After Previous Subtask). In sequential mode, the process waits until the previous subtask is finished before starting the next one. This is only available for AutoGrid™, Design3D and the FINE™/Turbo solver subtasks. Only a certain amount of tasks can be performed at the same time depending on the available licenses. The subtasks related to postprocessing with CFView™ are always executed in sequential mode. c) Remote Copy The Remote copy to option allows the user to specify that the files are not visible from the remote machine and must be transferred. This is only available for AutoGrid™, Design3D and the FINE™/Turbo solver. d) Launching Mode The FINE™/Turbo solver has an integrated multiprocessor machine concept, which allows the user to launch the flow solver in serial mode or parallel mode. FINE™/Turbo provides two parallel versions of the flow solver: Parallel Computation relies on the existing block structure and Parallel Partitioned Computation allows to automatically split the mesh in order to run the computation on a massively parallel environment, see Chapter 11-4 for more information. d.1) Sequential Computation By default, the FINE™/Turbo solver will be launched in serial mode. Nothing is needed to set a sequential computation. d.2) Parallel Computation - MPI system The option Parallel Computation can be selected to specify that the parallel version of the flow solver has to be used for this computation. The button Parallel Settings gives access to the dialog box used to set up a parallel computation. When the dialog box is opened, the block list displays all the blocks of the mesh. The user can define new processes on all the available machines. Additionally, the load balancing can be defined manually or automatically (by using the Automatic Load Balancing button). The parallel processing can only be used on multiprocessor machine (shared memory mode) or on machines with the same operating systems (homogenous distributed memory mode) See section 11-4 for more detailed information on parallel computations. FINE™/Turbo 11-9 Task Manager The Task Manager Interface Processes list with the load balancing of the cells Buttons used to remove or add new processes on the specified machine List of the block in the associated mesh Button used to link the selected block with a process Default block distribution Button used to allocate more memory FIGURE 11.3.2-4 Parallel settings - load balancing d.3) Parallel Computation - Queuing system Within the Task Manager, the parallel computation can also be set-up on the Sun Grid Engine batch system (SGE), the Portable Batch System (PBS) or the Load Sharing Facility (LSF). When setting a parallel computation on a queuing system, the option Parallel Computation has to be selected and the button Queuing system has to be activated. The button Parallel Settings gives access to the dialog box used to set up a parallel computation on a queuing system. After the dialog box is opened, the block list displays all the blocks of the mesh, see Figure 11.3.25. When a queuing system is used, the number of processors and the system environment have to be specified. Depending on the number of processors, the load balancing can be defined automatically (by using the Automatic Load Balancing button) or manually. 11-10 FINE™/Turbo The Task Manager Interface Task Manager Impose the number of processors Default block distribution Processes list with the load balancing of the cells List of the block in the associated mesh Button used to link the selected block with a process SGE/PBS/LSF environment SGE/PBS/LSF template Button used to allocate more memory FIGURE 11.3.2-5 Parallel settings - load balancing for SGE/PBS/LSF d.3.1) SGE system The SGE system includes the possibility to add a SGE type host and to define arguments needed to launch the computation within the Task Manager. Host Definition In the page Hosts definition the user needs to add the host. When adding the host, automatic checks are performed: 1. it will detect if the "sge_qmaster" or "sge_execd" is running on the platform. If not, it means that the platform does not have SGE capabilities. 2. it will detect all parallel environments defined in SGE. 3. it will detect all parallel environments, that the user is allowed to use. If no parallel environment could be accessed by the user, his login should be added to the user list by the SGE administrator. When all checks are successful, the SGE capability of the added host is activated and the user can see if the host added is a SGE platform within the Task Manager GUI (Figure 11.3.1-1). Task Definition If the user selects a SGE platform when launching an FINE™/Turbo solver task in parallel, the Task Definition page gives access to the MPI or SGE system. When the SGE system is used, the task can be defined as shown in Figure 11.3.2-5. The user can change the block distribution but not the process host names since the FINE™/Turbo 11-11 Task Manager The Task Manager Interface SGE system only asks for a number of processors. See section 11-4 for more detailed information on parallel computations. Process Management Once the process is starting, the ".run" file is modified automatically, depending on the number of processors used. A script file (".sge") is also created at the same time as the ".p4pg" file, when using MPI system. The name of the SGE job is limited to 8 characters and the following format is thus chosen "comp####" where #### stands for any number depending of the number of SGE jobs already running under the same environment. Because the FINE™/Turbo solver has not been launched using the PVM daemon, there is no communication with the Task Manager. To test if a computation is running, the "qstat" command with the job-ID number of the SGE job is used. To suspend the SGE job, the user can use the Suspend function of the Task Manager. It will create automatically a ".stop" file in the running computation directory that will enable the FINE™/Turbo solver to suspend after saving the solution at the next iteration or after the full multigrid initialization. To kill the SGE job, the user can use the Kill function. The Task Manager will then use the SGE’s function "qdel" to kill the computation without saving the solution. To kill the FINE™/Turbo solver properly, the SGE’s "execd parameters" variable should be set to "NOTIFY_KILL=TERM" and the "notify time" variable of nodes should be set to a sufficient value to allow the FINE™/Turbo solver to exit properly (e.g. 120 seconds). In general, this variable should be set to a value higher than the time required for 1 iteration. We advise the user to ask the SGE administrator to check these variables. d.3.2) PBS system The PBS system includes the possibility to add a PBS type host and to define the arguments needed to launch the computation within the Task Manager. Host Definition In the page Hosts definition the user needs to add the host. When adding the host, automatic checks are performed: 1. it will detect if the process "pbs_mom" is running on the platform. If not, it means that the platform does not have PBS capabilities. 2. it will detect all defined PBS environments. When all checks are successful, the PBS capability of the added host is activated and the user can see if the host added is a PBS platform within the Task Manager GUI (Figure 11.3.1-1). Task Definition If the user selects a PBS platform when launching an FINE™/Turbo solver task in parallel, the Task Definition page gives access to the MPI or PBS system. When the PBS system is used, the task can be defined as shown in Figure 11.3.2-5. The user can change the block distribution but not the process host names since the PBS system only asks for a number of processors. Process Management 11-12 FINE™/Turbo The Task Manager Interface Task Manager Once the process is starting, the ".run" file is modified automatically, depending on the number of processors used. A script file (".pbs") is also created at the same time as the ".p4pg" file, when using MPI system. The name of the PBS job is limited to 8 characters and the following format is thus chosen "comp####" where #### stands for any number depending of the number of PBS jobs already running under the same environment. Because the FINE™/Turbo solver has not been launched using the PVM daemon, there is no communication with the Task Manager. To test if a computation is running, the "qstat" command with the job-ID number of the PBS job is used. To suspend the PBS job, the user can use the Suspend function of the Task Manager. It will create automatically a ".stop" file in the running computation directory that will enable the FINE™/Turbo solver to suspend after saving the solution at the next iteration or after the full multigrid initialization. To kill the PBS job, the user can use the Kill function. The Task Manager will then use the PBS’s function "qdel" to kill the computation without saving the solution. To kill the FINE™/Turbo solver properly, the PBS variable "kill_delay" should be set to a sufficiently high value to allow the FINE™/Turbo solver to exit properly (e.g. 120 seconds). In general, this variable should be set to a value higher than the time required for 1 iteration. We advise the user to ask the PBS administrator to check this variable. d.3.3) LSF system The LSF system includes the possibility to add a LSF type host and to define the arguments needed to launch the computation within the Task Manager. Host Definition In the page Hosts definition the user needs to add the host. When adding the host, automatic checks are performed: 1. it will detect if the process "sbatchd" is running on the platform. If not, it means that the platform does not have LSF capabilities. 2. it will detect all defined LSF environments. When all checks are successful, the LSF capability of the added host is activated and the user can see if the host added is a LSF platform within the Task Manager GUI (Figure 11.3.1-1). Task Definition If the user selects a LSF platform when launching an FINE™/Turbo solver task in parallel, the Task Definition page gives access to the MPI or LSF system. When the LSF system is used, the task can be defined as shown in Figure 11.3.2-5. The user can change the block distribution but not the process host names since the LSF system only asks for a number of processors. Process Management Once the process is starting, the ".run" file is modified automatically, depending on the number of processors used. A script file (".lsf") is also created at the same time as the ".p4pg" file, when using MPI system. The name of the LSF job is limited to 8 characters and the following format is thus chosen "comp####" where #### stands for any number depending of the number of LSF FINE™/Turbo 11-13 Task Manager The Task Manager Interface jobs already running under the same environment. Because the FINE™/Turbo solver has not been launched using the PVM daemon, there is no communication with the Task Manager. To test if a computation is running, the "bjobs" command with the job-ID number of the LSF job is used. To suspend the LSF job, the user can use the Suspend function of the Task Manager. It will create automatically a ".stop" file in the running computation directory that will enable the FINE™/Turbo solver to suspend after saving the solution at the next iteration or after the full multigrid initialization. To kill the LSF job, the user can use the Kill function. The Task Manager will then use the LSF’s function "bkill" to kill the computation without saving the solution. To kill the FINE™/Turbo solver properly, the LSF variable "JOB_TERMINATE_INTERVAL" should be set to a sufficiently high value to allow the FINE™/Turbo solver to exit properly (e.g. 120 seconds). In general, this variable should be set to a value higher than the time required for 1 iteration. We advise the user to ask the LSF administrator to check this variable. d.4) Parallel Partitioned Computation - MPI system The option Parallel Partitioned Computation can be selected to specify that the parallel partitioned version of the flow solver has to be used for this computation. The button Parallel Partitioned Settings gives access to the dialog box used to set up a parallel partitioned computation. FIGURE 11.3.2-6 Parallel partitioned settings For parallel partitioned computation, the mesh will be automatically partitioned. What the user needs to do is to define the hosts with the number of processes and to specify the parameters used to split and partition the mesh. On the left side of the parallel partitioned settings dialog, the hosts can be added or removed. The list shows all the defined hosts and its processes. The button New Process(es) on allows to add the 11-14 FINE™/Turbo The Task Manager Interface Task Manager specified number of processes (left of the button) on the selected host (right of the button) to the host list. The button Remove Selected Host And Its Processes allows to remove the selected host from the list. For the partition, the user needs to specify the Target load balance efficiency, which is a real between [0,1]. More the target load balance efficiency is close to 1, more the workload, the communications,... will be properly balanced over the processes but more sub blocks will compose the partition. In order to keep the computational efficiency, the maximum number of blocks per process is limited to 8 in the parallel partitioned computation. So, if the user specify a large target load balance efficiency, a partition will be proposed even if it does not raise the expected balancing. If the option Split block into two subblocks (n subblocks otherwise) is activated, the block will be split into two subblocks when splitting. Otherwise the block will be split into n subblocks (depending on the case). After setting the parameters, click-left on the button Apply Virtual Partitioning to launch the symbolic partitioning and balancing algorithm. The status of the partitioning algorithm can be checked by clicking on the button Partitioning Status>>. The parallel processing can only be used on multiprocessor machine (shared memory mode) or on machines with the same operating systems (homogenous distributed memory mode) See section 11-4 for more detailed information on parallel partitioned computations. d.5) User-defined Templates on Queuing Systems If the option Queuing system in the Task Definition page is activated, the user needs to select a template in the Parallel settings dialog box in order to submit the computation to the queue. By default, a set of templates is available for the supported queuing systems SGE, PBS and LSF (with corresponding extension .sge, .pbs or .lsf). The user can also create a new template to customize the settings: queuing system environment, OpenMPI, etc. In order to use an user-defined template, the user has to: • name the new template using the extension .sge, .pbs or .lsf, corresponding to the queuing system, • copy the template to the queuing templates folder: — On Unix/Linux systems: "NUMECA_INSTALLATION_DIRECTORY/fine#/COMMON/queuing_templates/" — On Windows systems: "NUMECA_INSTALLATION_DIRECTORY\Fine#\bin\queuing_templates\" It is strongly suggested to create a new template based on the existing templates. All the existing templates can be found in the queuing templates folder mentioned above. Figure 11.3.2-7 shows the contents of the default SGE template launching the single precision solver. Based on this template, the user can customize the SGE environment, the OpenMPI settings and the command launching the computation. Please refer to Chapter 11-5.5.3 to Chapter 11-5.5.5 for the detailed explanation of the template contents. The user must obey the following rules when creating a new template: • Any line beginning with # (except #!, #$, #PBS and #BSUB) is a comment. FINE™/Turbo 11-15 Task Manager The Task Manager Interface • The first blank line MUST be placed after the section defining queuing system environment and before the section defining the OpenMPI settings. Here, TaskManager will define the queuing system environment variables (number of processors, name of the computation, etc.) and the NUMECA variables (NI_VERSION_DIR and NUMECA_SOFT_VERSION), depending on the user-settings in TaskManager. • The comment line "# COMPUTATION SETTINGS" MUST be kept and placed before the command launching the flow solver. Here, TaskManager will define the computation settings (variables RUN_FILE, STEERING1 and STEERING2), which are used in the command launching the flow solver. Define SGE environment Variables The first blank line Define OpenMPI variables Comment line where computation setting will be defined Command launching the flow solver FIGURE 11.3.2-7 The 11-16 default template launching the single precision solver for SGE (default.sge) FINE™/Turbo Parallel Computations Task Manager e) Message Window When a task is started, a Task Manager process is launched to take care about the task management: process communication, automatic launching of the sequential and parallel subtasks. A message window linked to the Task Manager is opened. In this window the user can follow the evolution of the status of all the subtasks of the current task. In case the flow solver is launched, the iterations are also displayed in this window as shown in Figure 11.3.2-8. At the bottom of the Task Manager window a Refresh Rate can be chosen. This rate determines how frequently the Task Manager window is updated. A higher refresh rate will update the information in the window more frequently but will use more of the available CPU. FIGURE 11.3.2-8 Task Manager information window If the user quits FINE™/Turbo, all the message windows will stay open and the tasks will continue. Closing a message window will immediately kill all the subtasks of the corresponding task. 11-4 Parallel Computations 11-4.1 Introduction Parallel computations can be defined through the FINE™/Turbo interface as described in section 11-3.2.3. Parallel processing relies on the distribution of independent tasks among several processors using communication protocols to transfer data from one processor to another whenever this is necessary. This induces of course an acceleration of the computation itself but it also offers the possibility to perform large computations, that would not fit on a single processor. The parallel version uses MPI (Message Passing Interface) libraries. MPI was chosen among other tools such as PVM or Open MP for its high communication performances (high bandwidth, low FINE™/Turbo 11-17 Task Manager Parallel Computations latencies). Although Open MP has better performance on shared memory configurations, i.e. on a given computer with single global memory and several processors, it is not designed for distributed memory configurations (several computers with their own memory). The parallel version is implemented for UNIX, LINUX and Windows platforms (see Installation Notes for more details on the way to establish connections between platforms). By default, FINE™/ Turbo uses the MPICH/MPICH2 libraries on Windows operating systems and the OpenMPI libraries v1.4 on LINUX/UNIX operating systems. The present MPI implementation is based on a host/slaves approach. One host process is dedicated to input/output management. The host reads the mesh and input files, sends the data to the computation processes (the slaves), receives the computation results from the slave processes and writes the output files. Figure 11.4.1-9 shows the task distribution on a 4 processor (1 host + 3 slaves) configuration. Note that the host/slaves implementation will be replaced progressively as parallel MPI input/output functionalities are now available. Input data base reading process 1 Host process 2 boundary conditions FIGURE 11.4.1-9 Tasks writing Output data base process 3 boundary conditions in a parallel computation FINE™/Turbo provides two kinds of parallel computation mode: Parallel Computation and Parallel Partitioned Computation, see section 11-3.2.3 for the interface to set Parallel Computation and Parallel Partitioned Computation. 11-4.1.1 Parallel Computation For parallel computation, the parallel processing relies on the block structure of the mesh. Each process is assigned a given number of blocks. As a consequence, the number of processors cannot exceed the number of blocks in the mesh. Boundary data are exchanged between processors each time an update of the flow solution is required. 11-4.1.2 Parallel Partitioned Computation The objective of Parallel Partitioned Computation is to improve the capabilities of FINE™/Turbo in a massively parallel environment, allowing the user to most effectively utilize the computational resources (large clusters especially). The current parallel partitioned computation version of the flow solver allows to efficiently use upwards of 1000 compute cores for a single analysis. The parallel partitioned computation version of the flow solver integrates automatic pre- and postprocessing modules. The pre-processing module is used to automatically split the original mesh and partition the mesh depending on the user defined Target load balance efficiency and the number of processes, see section 11-3.2.3. The post-processing module is used to output the result based on the original mesh instead of on the thousands of split blocks. 11-18 FINE™/Turbo Parallel Computations Task Manager The parallel partitioned computation is not compatible with the following modules: • transition module • cooling holes (except the type Points) • R/S interface: Conservative Coupling by Pitchwise Row / Local Conservative Coupling • FNMB connecting fluid and solid blocks • phase lagged method • 2D or axi-symmetric projects • Lagrangian module • Turbo machinery initial solution linked to AG4 mesh (expert parameter INITRB set to 0) • Moving grid module 11-4.2 Management of Inter-Block Communication The block structure of the solver allows to distribute blocks across processors or computers (in case of a cluster). Each processor will handle an integer number of blocks. The treatment of the boundary condition will be replaced by a message passing between the processors or remote computers. Communication optimization The parallel version of the flow solver is optimized in order to minimize duplicated data as well as the number and the volume of exchanged messages. A significant improvement of the code performance was obtained by grouping small messages into larger buffers: the information contained in small messages is usually shared by a large number of blocks, leading to frequent messages of that type. This is the case for block edges data that are exchanged several times during each iteration. Significant latency times are induced by these communication processes and message grouping highly reduces the number of such messages. Large message limitation Very large messages are usually exchanged during initialization and at the end of the computation between the nodes and the host. These also need to be avoided as they can cause important memory needs and eventually lead to system failure. Messages are split into buffers of maximum size MXBFSZ (see section 11-4.3) in order to avoid excessive MPI memory requests. 11-4.3 How to Run a Parallel Computation Configuring a parallel run using the FINE™/Turbo interface is described in section 11-3.2.3. Memory allocation Memory allocation is performed as follows: • The integer data structure is duplicated for all processes. Since the integer data structure size is about a tenth of the real data structure, this does not lead to high memory overload when the number of processes is less than 10. • The real memory allocation is performed for each process. It should be set to the minimal amount of memory necessary to hold the data structure on the process that has most grid points. When the load is well balanced, the real memory overload is due to face and edge data structures. These data need indeed to be duplicated when two processors are involved in the same block connection. FINE™/Turbo 11-19 Task Manager Parallel Computations The total memory need Mtotal for a parallel computation involving n ( n ≥ 2 ) processors can be estimated as: n M total = M real ⋅ 1.2 ⋅ ------------ + M integer ⋅ n n–1 where Mreal and Minteger are the real and integer memory needed for the same computation in sequential mode. From a practical point of view, the user does not specify the total memory needed but the integer M real - ⋅ 1.2 for the real memand real memory required per processor. This can be estimated as -------------- n ory and Minteger for the integer memory. When doing a parallel calculation, the estimated real memory displayed by FINE™/ Turbo on the Control Variables page, shall not be followed but the formula shown above will be respected. The following table states the total memory needed for a parallel computation using respectively 4 and 6 and 8 processors. The values of Mreal and Minteger are set to 10 Mb and 1 Mb respectively. The equivalent memory request on a single processor is thus 11Mb. n Mtotal (Mb) Parallel overhead (Mb) 4 20 9 6 20.4 9.4 8 21.7 10.7 TABLE 11-1 Parallel memory request In the present implementation, the presence of the host processor increases the global memory request. It also reduces the overall speed-up of the computation as it is mainly dedicated to I/O management and no computation is affected to it. Future versions of the FINE™/Turbo solver will optimize this aspect by removing gradually the need of a host processor. Message size limitation During initialization and final steps, large messages are usually exchanged between the nodes and the host process. In order to avoid any system failure, messages are split into buffers of maximum size. This size is set to 100000 by default but the user can eventually tune this value through the expert parameter MXBFSZ. 11-4.4 Use an External OpenMPI Library on LINUX/UNIX By default, FINE™/Turbo uses the OpenMPI library v1.4 on LINUX/UNIX operation systems. FINE™/Turbo also allows to use an external OpenMPI library, which may be a tuned, customized or hardware specific OpenMPI library. In order to use an external library, the user has to re-define the runtime environment, which can be done in two ways: • create a file ".default_mpi’" under the folder / fine#/_mpi/, where # is the FINE™/Turbo version. Then edit the file ".default_mpi" and specify the external OpenMPI library in the file ".default_mpi" (here the external library is located in /tmp/libs/OpenMPI/ompi1.4): — for csh or tcsh: setenv NI_MPI_DEFAULT ompi 11-20 FINE™/Turbo Parallel Computations Task Manager setenv NUMECA_MPI_DIR /tmp/libs/OpenMPI/ompi1.4 — for bash or ksh: export NI_MPI_DEFAULT=ompi export NUMECA_MPI_DIR=/tmp/libs/OpenMPI/ompi1.4 In this way, the FINE™/Turbo flow solver will use the specified external library when launching computations. • create a file "default_mpi’" under the folder $HOME/.numeca/, where $HOME is the home directory of the user account. Then edit the file "default_mpi" and specify the external OpenMPI library in the file "default_mpi" (here the external library is located in /tmp/libs/ OpenMPI/ompi1.4): — for csh or tcsh: setenv NI_MPI_DEFAULT ompi setenv NUMECA_MPI_DIR /tmp/libs/OpenMPI/ompi1.4 — for bash or ksh: export NI_MPI_DEFAULT=ompi export NUMECA_MPI_DIR=/tmp/libs/OpenMPI/ompi1.4 In this way, all the NUMECA flow solvers running in this user account will use the specified external library. 11-4.5 Troubleshooting Sometimes the parallel computations using MPI can not be started and displays the error message "p2_3150: p4_error: alloc_p4_mes failed: 0" in the std file. This may be coming from the insufficient default value of the environment variable P4_GLOBMEMSIZE of your linux system. In that case the user can increase the value in the shell before starting FINE by typing the following: • for csh or tcsh: setenv P4_GLOBMEMSIZE 50000000 • for bash or ksh: export P4_GLOBMEMSIZE=50000000 Sometimes the parallel computations using MPI might hang or crash at unpredictable iteration that displays the error message "net_recv_failed for fd" in the std file. The user can increase the value of the environment variable P4_SOCKBUFSIZE before starting FINE in order to reduce the amount of occurrences of this problem. Set this variable in the shell by typing the following: • for csh or tcsh: setenv P4_SOCKBUFSIZE 1024000 • for bash or ksh: export P4_SOCKBUFSIZE=1024000 Of course the settings of the P4_GLOBMEMSIZE and P4_SOCKBUFSIZE can be added to the ".cshrc", ".tcshrc", ".bashrc" or ".profile" file of the user. If the user launch the computation in batch mode or on a cluster by using a script, this variable can be also modified in the launch script before launching the computation. Please notice that you need to stop or kill all pvm daemons to make sure that this change is taken into account. This can be done as follows: • Rebooting your machine if possible, or • In the Task Manager/Host Definition to click on Shutdown to clean the pvm, or • To kill the pvm by typing in the shell kill -9 id_pvmd3. By killing the pvm or performing a shutdown all the processes (including other softFINE™/Turbo 11-21 Task Manager Task Management in Batch ware that is using PVM) will be stopped. If the computation is interrupted for the other unknown reason, more detailed information is provided in the ".std" and ".log" computation files. These files contain all relevant information, including MPI error messages and can be sent to our local support office. 11-4.6 Limitations • The distributed memory mode is restricted to homogeneous (i.e. with the same operating system) clusters. • The blank space is not allowed in the path name. 11-5 Task Management in Batch This section provides the necessary information to launch NUMECA software from a shell, without using the IGG™, AutoGrid™, FINE™/Turbo or CFView™ interfaces. Every time the ".run" file of a FINE™/Turbo computation is saved, a script file is automatically created. On UNIX systems, the name of this file has the extension ".batch". On Windows the extension is ".bat". Such files contain text lines with the commands to launch the software with the appropriate command arguments. To launch a task from a shell simply execute the automatically generated file by typing its name in a shell. In the next sections the available commands to launch NUMECA software are described in more detail. The capability to launch in batch is currently not supported for the FINE™/Turbo solver in parallel mode on PC. 11-5.1 Launch IGG™ in Batch 11-5.1.1 How to Launch IGG™ on UNIX To launch IGG™ without use of the interface the commands to perform must be written in a macro script file. To create such a file: 1. Create a script file ".py". For more details on the commands that can be included in such a script file see the IGG™ manual. 2. Launch the macro script in a shell by typing: "igg /script.py -batch -niversion " The command line to start the grid generator IGG™ contains its name, the full path of the script ".py" file ( ) to launch and the IGG™ release ( ) that will be used. The "batch" option avoids the display of the IGG™ graphical user interface. When launched in batch, IGG™ does not open the graphical user interface but an access to the display of the machine on which the process is launched, is still required. 11-22 FINE™/Turbo Task Management in Batch Task Manager 11-5.1.2 How to Launch IGG™ on Windows 1. Create script file ".py". For more detailed information on the commands to include in a macro script see the IGG™ manual. 2. Launch the macro script ".py" by typing in a DOS-shell: " \igg.exe -script \script.py -batch" The command line to start the grid generator IGG™ contains the full path name of the igg.exe executable ( ) and the full path of the script ".py" file ( ) to launch. The "script" & "-batch" options respectively permit to launch the script and to avoid to display the IGG™ graphical user interface. The igg.exe executable can be found in: " \Fine#\bin\" When launched in batch, IGG™ does not open the graphical user interface but an access to the display of the machine on which the process is launched, is still required. Remarks: • The full path of the executable (igg.exe) has to be specified. • The full path of the script has to be specified. • There can be a segmentation fault at exit (due to an uncontrollable "opengl" problem). It is possible to avoid this message, by adding the option "-driver msw". 11-5.2 Launch AutoGrid™ in Batch 11-5.2.1 How to Launch AutoGrid™ 4 on UNIX 1. Create a template and geometry file (".trb" and ".geomTurbo") using the AutoGrid™ 4 interface. Start AutoGrid™ to create a mesh from these files by typing in a shell: "igg -batch -autoGrid /test.trb /test.geomTurbo \\ /test.igg -niversion " The command line to start the grid generator AutoGrid™ 4 contains its name, the full path of the template and geometry file ( ), the full path of the mesh that will be saved and the IGG™ version that will be used. The "-batch" option avoids the display of the IGG™ graphical user interface. 2. When launched in batch, IGG™ does not open the graphical user interface but an access to the display of the machine on which the process is launched, is still required. 11-5.2.2 How to Launch AutoGrid™ on UNIX 1. Create a template and geometry files (".trb" and ".geomTurbo") using the AutoGrid™ interface. 2. Start AutoGrid™ to create a mesh from these files by typing in a shell: "igg -batch -autogrid5 -trb /test.trb -geomTurbo /test.geomTurbo -mesh /test.igg -niversion " \\ The command line to start the grid generator AutoGrid™ contains its name, the full path of the template and geometry file ( ), the full path of the mesh that will be saved and the IGG™ version that will be used. The "-batch" option avoids the display of the IGG™ graphical user interface. When launched in batch, IGG™ does not open the graphical user interface but an access to the display of the machine on which the process is launched, is still required. FINE™/Turbo 11-23 Task Manager Task Management in Batch 11-5.2.3 How to Launch AutoGrid™ 4 on Windows 1. Create a template and geometry files (".trb" and ".geomTurbo") using the AutoGrid™ 4 interface. 2. Start AutoGrid™ 4 to create a mesh from these files by typing in a DOS-shell: " \igg.exe -batch -autoGrid \template.trb \template.geomTurbo \mesh.igg" \\ The command line to start the grid generator AutoGrid™ 4 contains the full path of the igg.exe executable ( ), the full path of the template and geometry file ( ) and the full path of the mesh that will be saved. The "-batch" option avoids the display of the IGG™ graphical user interface. The igg.exe executable can be found in: " \Fine#\bin\" When launched in batch, IGG™ does not open the graphical user interface but an access to the display of the machine on which the process is launched, is still required. 11-5.2.4 How to Launch AutoGrid™ on Windows 1. Create a template and geometry files (".trb" and ".geomTurbo") using the AutoGrid™ interface. 2. Start AutoGrid™ to create a mesh from these files by typing in a DOS-shell: " \igg.exe -batch -autogrid5 -trb \template.trb\\ -geomTurbo /template.geomTurbo -mesh /mesh.igg" The command line to start the grid generator AutoGrid™ contains the full path of the igg.exe executable ( ), the full path of the template and geometry file ( ) and the full path of the mesh that will be saved. The "-batch" option avoids the display of the IGG™ graphical user interface. The igg.exe executable can be found in: " \Fine#\bin\" When launched in batch, IGG™ does not open the graphical user interface but an access to the display of the machine on which the process is launched, is still required. 11-5.3 Launch FINE™ in Batch The user has the possibility to set-up a computation, without opening the FINE™/Turbo interface, through the finebatch program. In batch mode, FINE™/Turbo will create a computation file (.run) from an existing project (.iec) and mesh (.igg) file. This method can be used to set-up sequential or parallel computations. If the geometry or mesh topology has been changed, it is strongly advised to use FINE™/Turbo interface to set-up the computation. When a new/modified mesh is linked with an existing project file, an automatic merge will be performed. This merge will reset the physical parameters to their default values for the modified parts of the mesh. If for example blocks have been added, the rotation speed, solid conductivity and initial solution of these blocks will be set to the default values. The user must have read/write permissions in the project directory. 11-5.3.1 How to Launch FINE™ on UNIX a) Create a ".run" file To link a new mesh to an existing project and create the corresponding ".run" file, the finebatch program can be launched with following command: 11-24 FINE™/Turbo Task Management in Batch Task Manager "fine -niversion -batch /project.iec /mesh.igg \\ /output.run /fine /COMMON \\ " or "fine -niversion -batch /project.iec /mesh.igg \\ /output.run " or "fine -batch /project.iec /mesh.igg\\ /output.run " In the command line, the version of FINE™/Turbo ( ) needs to be specified, together with the -batch option. The -batch option requires following arguments: • Full path of the input project file (.iec) • Full path of the input mesh file (.igg) • Full path of the output computation file (.run) • Full path of the euranus.def file. This is an optional argument, if no value is specified the COMMON path of the specified version will be used. • Index of the computation in the project file. This is an optional argument, if no value is specified the first computation will be used. b) Set-up a parallel computation using MPI To set-up a parallel computation using MPI, the finebatch program can be launched with following command: "fine -niversion -batch -parallel /computation/computation.run -print" or "fine -batch -parallel /computation/computation.run -print" In the command line, the version of FINE™/Turbo ( ) needs to be specified, together with the -batch and the -parallel option. The -print option is used to print the output to the screen. The batch -parallel option require following arguments: • Full path of the input computation file (.run) • Number of machines to be used for the parallel computation • Machine name and the number of processors to use on that machine. If = N, the machine name and the number of processors have to be repeated N times. e.g. Parallel computation using 2 machines and 3 processors on each machine: "fine87_1 -batch -parallel /user/computation/computation.run 2 machine_1 3 machine_2 3" By default, the distribution of blocks per processor is performed automatically. This automatic distribution can be modified by adding "-interactive" to the command line. An automatic distribution will then be proposed, which can be modified by the user. The output of the program contains 3 files: • Modified computation file (.run) • Script file to launch the computation, see section 11-5.5.1 for more details • Host definition file (.p4pg), see section 11-5.5.1 for more details FINE™/Turbo 11-25 Task Manager Task Management in Batch When generating the parallel computation files, the p4pg file generated uses the local machine as master process and the machines specified in the argument as computing processes c) Set-up a parallel computation using SGE To set-up a parallel computation using the SGE system, the finebatch program can be launched with following command: "fine -niversion -batch -sge /computation/computation.run\\ -print" or "fine -batch -sge /computation/computation.run\\ -print" In the command line, the version of FINE™/Turbo ( ) needs to be specified, together with the -batch and the -sge option. The -print option is used to print the output to the screen. The -batch -sge option require following arguments: • Full path of the input computation file (.run) • SGE environment to be used for the parallel computation • Number of processors to be used for the parallel computation • Name of template file generated by the user. (It is optional. Finebatch will use the default template file by default.) The distribution of blocks per processor is performed automatically. The output of the program contains 2 files: • Modified computation file (.run) • SGE script file (.sge) to launch the computation, see section 11-5.5.3 for more details d) Set-up a parallel computation using PBS To set-up a parallel computation using the PBS system, the finebatch program can be launched with following command: "fine -niversion -batch -pbs /computation/computation.run\\ -print" or "fine -batch -pbs /computation/computation.run\\ -print" In the command line, the version of FINE™/Turbo ( ) needs to be specified, together with the -batch and the -pbs option. The -print option is used to print the output to the screen. The -batch -pbs option require following arguments: • Full path of the input computation file (.run) • PBS environment to be used for the parallel computation • Number of processors to be used for the parallel computation • Name of template file generated by the user. (It is optional. Finebatch will use the default template file by default.) The distribution of blocks per processor is performed automatically. The output of the program contains 2 files: 11-26 FINE™/Turbo Task Management in Batch Task Manager • Modified computation file (.run) • PBS script file (.pbs) to launch the computation, see section 11-5.5.4 for more details e) Set-up a parallel computation using LSF To set-up a parallel computation using the LSF system, the finebatch program can be launched with following command: "fine -niversion -batch -lsf /computation/computation.run\\ -print" or "fine -batch -lsf /computation/computation.run\\ -print" In the command line, the version of FINE™/Turbo ( ) needs to be specified, together with the -batch and the -lsf option. The -print option is used to print the output to the screen. The -batch lsf option require following arguments: • Full path of the input computation file (.run) • LSF environment to be used for the parallel computation • Number of processors to be used for the parallel computation • Name of template file generated by the user. (It is optional. Finebatch will use the default template file by default.) The distribution of blocks per processor is performed automatically. The output of the program contains 2 files: • Modified computation file (.run) • LSF script file (.lsf) to launch the computation, see section 11-5.5.5 for more details f) Set-up a parallel partitioned computation using MPI To set-up a parallel partitioned computation using MPI, the finebatch program can be launched with following command: "fine -niversion -batch -partition -parallel /computation/computation.run