OpenFOAM Tutorial. [ ] Numerical Methods in Fluid Dynamics. Finite Volume Method, Dictionary Syntax, and Implementation Details

Transcription

1 [ ] Numerical Methods in Fluid Dynamics Tutorial Finite Volume Method, Dictionary Syntax, and Implementation Details Univ. Assist. MSc. Francesco Romanò December 11th, 2014

2 Outline 1 [ ] Univ. Assist. MSc. Francesco Romanò 2/32

3 Description of the Software : Description of the Software The CFD Toolbox is a free, open source CFD software package which solves using a collocation FVM; [ ] Univ. Assist. MSc. Francesco Romanò 3/32

4 Description of the Software : Description of the Software The CFD Toolbox is a free, open source CFD software package which solves using a collocation FVM; It can solve complex fluid flows involving chemical reactions, turbulence and heat transfer, solid dynamics and electromagnetics and includes tools for meshing, preand post-processing; [ ] Univ. Assist. MSc. Francesco Romanò 3/32

5 Description of the Software : Description of the Software The CFD Toolbox is a free, open source CFD software package which solves using a collocation FVM; It can solve complex fluid flows involving chemical reactions, turbulence and heat transfer, solid dynamics and electromagnetics and includes tools for meshing, preand post-processing; Almost everything runs in parallel as standard; [ ] Univ. Assist. MSc. Francesco Romanò 3/32

6 Description of the Software : Description of the Software The CFD Toolbox is a free, open source CFD software package which solves using a collocation FVM; It can solve complex fluid flows involving chemical reactions, turbulence and heat transfer, solid dynamics and electromagnetics and includes tools for meshing, preand post-processing; Almost everything runs in parallel as standard; offers users possibility to customise and extend the existing functionality. [ ] Univ. Assist. MSc. Francesco Romanò 3/32

7 [ ] Univ. Assist. MSc. Francesco Romanò 4/32 : <problem_folder>/constant/polymesh/ initial banner: /* *- C++ -* *\ ========= \\ / F ield : The Open Source CFD Toolbox \\ / O peration Version: \\ / A nd Web: \\/ M anipulation \* */ FoamFile: sub-dictionary delimited by curly brackets containing code s information: FoamFile version 2.0; format ascii; class dictionary; object ; // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

8 [ ] Univ. Assist. MSc. Francesco Romanò 5/32 : <problem_folder>/constant/polymesh/ scaling parameter: converttometers 0.1; vertices: function delimited by parenthesis specifying Cartesian coordinates of the domain vertices 1 : vertices ( (0 0 0) (1 0 0)... ( ) ( ) ); 1 For 2 D cases, it is necessary to indicate suitable BCs.

9 : <problem_folder>/constant/polymesh/ blocks: function specifying how many mesh blocks form the discrete domain and their properties. hex: function specifying the vertices of this block. simplegrading: function specifying how to distribute the mesh. The ratio between the first and the last element of the mesh block is setted 1 for each direction: it means it is used a constant discretization in x, y ( and z ). blocks ( hex( )( )simpleGrading(1 1 1) ); [ ] Univ. Assist. MSc. Francesco Romanò 6/32

10 : <problem_folder>/constant/polymesh/ edges: tool that defines all the non straight edges. edges ( ); edges: There are different sort of definable edges: arc, simplespline, polyline, etc... arc: sort of edge which defines a circular arc, (in this case between nodes 0 and 5, and passing through the point in parenthesis). edges ( arc 0 5 ( ) ); [ ] Univ. Assist. MSc. Francesco Romanò 7/32

11 : <problem_folder>/constant/polymesh/ boundary: function specifying name, type and faces of each sub-bound. They are delimited by curly brackets after each of their name. boundary ( <NameOfTheBoundary> type <TypeOfTheBoundary>; faces ( (<4EdgesOfTheCurrentFace>) ); ); [ ] Univ. Assist. MSc. Francesco Romanò 8/32

12 : <problem_folder>/constant/polymesh/ type: type of the boundary that can be wall, empty, patch, etc... mergepatchpairs: tool that defines a list of patches to be meshed using a reciprocal correspondence of master and slave. mergepatchpairs ( ); // ***************************************** // running commands: <problem\_folder>$ blockmesh [ ] Univ. Assist. MSc. Francesco Romanò 9/32

13 [ ] Univ. Assist. MSc. Francesco Romanò 10/32 : <problem_folder>/0/p initial banner: /* *- C++ -* *\ ========= \\ / F ield : The Open Source CFD Toolbox \\ / O peration Version: \\ / A nd Web: \\/ M anipulation \* */ FoamFile: sub-dictionary delimited by curly brackets containing code s information: FoamFile version 2.0; format ascii; class volscalarfield; object p; // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

14 : <problem_folder>/0/p dimensions of the system: dimensions [ ]; % m^2/s^2 internalfield: it can be uniform (only one value) or not (scalar point-wise field) internalfield uniform 0; [ ] Univ. Assist. MSc. Francesco Romanò 11/32

15 : <problem_folder>/0/p boundaryfield: function containing boundary conditions referred to the name already used creating the mesh. boundaryfield <NameOfTheBoundary> type <TypeOfTheBoundaryCondition>; // ***************************************** // type: type of the boundary condition that can be zerogradient, fixedvalue, empty, etc... [ ] Univ. Assist. MSc. Francesco Romanò 12/32

16 [ ] Univ. Assist. MSc. Francesco Romanò 13/32 : <problem_folder>/0/u initial banner: /* *- C++ -* *\ ========= \\ / F ield : The Open Source CFD Toolbox \\ / O peration Version: \\ / A nd Web: \\/ M anipulation \* */ FoamFile: sub-dictionary delimited by curly brackets containing code s information: FoamFile version 2.0; format ascii; class volvectorfield; object U; // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

17 : <problem_folder>/0/u dimensions of the system: dimensions [ ]; % m/s internalfield: it can be uniform (only one vectorial value) or not (vectorial point-wise field) internalfield uniform (0 0 0); [ ] Univ. Assist. MSc. Francesco Romanò 14/32

18 : <problem_folder>/0/u boundaryfield: function containing boundary conditions referred to the name already used creating the mesh. boundaryfield <NameOfTheBoundary> type <TypeOfTheBoundaryCondition>; // ***************************************** // type: type of the boundary condition that can be zerogradient, fixedvalue, empty, etc... [ ] Univ. Assist. MSc. Francesco Romanò 15/32

19 [ ] Univ. Assist. MSc. Francesco Romanò 16/32 : <problem_folder>/constant/ initial banner: /* *- C++ -* *\ ========= \\ / F ield : The Open Source CFD Toolbox \\ / O peration Version: \\ / A nd Web: \\/ M anipulation \* */ FoamFile: sub-dictionary delimited by curly brackets containing code s information: FoamFile version 2.0; format ascii; class dictionary; location "constant" object ; // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

20 : <problem_folder>/constant/ physical properties of the system 2 : nu nu [ ] 0.01; % m^2/s // **************************************** // 2 In the case of incompressible single-phase flows, just kinematic viscosity has to be defined. Other properties should be eventually included in the dictionary. [ ] Univ. Assist. MSc. Francesco Romanò 17/32

21 [ ] Univ. Assist. MSc. Francesco Romanò 18/32 : <problem_folder>/system/ initial banner: /* *- C++ -* *\ ========= \\ / F ield : The Open Source CFD Toolbox \\ / O peration Version: \\ / A nd Web: \\/ M anipulation \* */ FoamFile: sub-dictionary delimited by curly brackets containing code s information: FoamFile version 2.0; format ascii; class dictionary; location "system"; object ; // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

22 [ ] Univ. Assist. MSc. Francesco Romanò 19/32 : <problem_folder>/system/ application: function that defines the model to use. application icofoam; startfrom: command used to set the initial time of the simulation. In this case the command is startime and, in the next row, it indicates that the simulation has t in = 0. The initial condition is then in a directory named 0. To use a previous calculation, instead of the command starttime, latesttime is used. startfrom starttime; starttime 0;

23 [ ] Univ. Assist. MSc. Francesco Romanò 20/32 : <problem_folder>/system/ stopat: command used to set the final time of the simulation. In this case the command is endtime and indicates that the simulation has t fin =.5. stopat endtime; endtime 0.5; deltat: defines the time step used for the simulation. Numerical stability problems can be due to time and the spatial discretization steps. Theoretically analysing the incompressible flow solver, the stability is controlled by the local Courant number, which has to be less than one. deltat 0.005;

24 [ ] Univ. Assist. MSc. Francesco Romanò 21/32 : <problem_folder>/system/ writecontrol: defines the kind of control used to save data. The command timestep saves each (writeinterval)x(time steps). The storage is in folders created using as name the time of saving. purgewrite: defines a limit on the number of storage directories: if the needed directories are more than the indicator, the previous data are cyclically overwritten. Not to define a limit purgewrite has to be 0. writecontrol timestep; writeinterval 20; purgewrite 0;

25 [ ] Univ. Assist. MSc. Francesco Romanò 22/32 : <problem_folder>/system/ further instruction for saving the data: writeformat ascii; writeprecision 6; writecompression off; timeformat general; timeprecision 6; runtimemodifiable true; // ***************************************** //

26 [ ] Univ. Assist. MSc. Francesco Romanò 23/32 : <problem_folder>/system/ initial banner: /* *- C++ -* *\ ========= \\ / F ield : The Open Source CFD Toolbox \\ / O peration Version: \\ / A nd Web: \\/ M anipulation \* */ FoamFile: sub-dictionary delimited by curly brackets containing code s information: FoamFile version 2.0; format ascii; class dictionary; location "system"; object ; // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

27 [ ] Univ. Assist. MSc. Francesco Romanò 24/32 : <problem_folder>/system/ ddtschemes: contains the information about the method to discretize the temporal derivative. Euler means that the time derivative is discretized using an Implicit Euler scheme. Other options are: CrankNicholson, backward, etc... ddtschemes default Euler;

28 [ ] Univ. Assist. MSc. Francesco Romanò 25/32 : <problem_folder>/system/ gradschemes: contains the information about the selected method to discretize the gradient. Gauss linear means that discretizes the gradient operator with the linear Gaussian method. Another method is the least squares method setting leastsquares instead of Gauss linear. gradschemes default grad(p) Gauss linear; Gauss linear;

29 : <problem_folder>/system/ divschemes and laplacianschemes: contains information about the selected method for discretizing the divergence and laplacian operators. divschemes default div(phi,u) laplacianschemes default none; Gauss linear; none; laplacian(nu,u) Gauss linear orthogonal; laplacian((1 A(U)),p) Gauss linear orthogonal; [ ] Univ. Assist. MSc. Francesco Romanò 26/32

30 [ ] Univ. Assist. MSc. Francesco Romanò 27/32 : <problem_folder>/system/ interpolationschemes: sets the interpolation method. interpolationschemes default linear; interpolate(hbya) linear; sngradschemes: sets the treatment for ( ), n. sngradschemes default orthogonal;

31 [ ] Univ. Assist. MSc. Francesco Romanò 28/32 : <problem_folder>/system/ fluxrequired: sets the information about fields for which is required to calculate a flux. fluxrequired default no; p ; // *************************************** //

32 [ ] Univ. Assist. MSc. Francesco Romanò 29/32 : <problem_folder>/system/ initial banner: /* *- C++ -* *\ ========= \\ / F ield : The Open Source CFD Toolbox \\ / O peration Version: \\ / A nd Web: \\/ M anipulation \* */ FoamFile: sub-dictionary delimited by curly brackets containing code s information: FoamFile version 2.0; format ascii; class dictionary; location "system"; object ; // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

33 [ ] Univ. Assist. MSc. Francesco Romanò 30/32 : <problem_folder>/system/ solvers: defines the set-up of the linear solvers. solvers <Var> solver preconditioner tolerance reltol <SolverType>; <PreconditionerType>; <AbsoluteTollerance>; <RelativeTollerance>;

34 : <problem_folder>/system/ <SplittingOperator>: defines the respective treatment of pressure and velocity. PISO ncorrectors 2; nnonorthogonalcorrectors 0; prefcell 0; prefvalue 0; // **************************************** // [ ] Univ. Assist. MSc. Francesco Romanò 31/32

35 a Case : a Case <problem_folder> running a solver in foreground: <problem_folder>$ <solvername> running a solver in background: <problem_folder>$ <solvername> > log & data visualization: <problem_folder>$ parafoam [ ] Univ. Assist. MSc. Francesco Romanò 32/32