[302.044] Numerical Methods in Fluid Dynamics …info.tuwien.ac.at/ViennaOpenFOAMUserGroup/9thb... · OpenFOAM Tutorial Finite Volume Method, Dictionary ... [email protected]

[302.044] Numerical Methodsin Fluid Dynamics

OpenFOAM TutorialFinite Volume Method, Dictionary Syntax,

and Implementation Details

Univ. Assist. MSc. Francesco Romanò

[email protected]

December 11th, 2014

mailto:[email protected]

Open FOAMblockMeshDictInitialConditionstransportPropertiescontrolDictfvSchemesfvSolutionRunningOpenFOAM

Outline

1 Open FOAMblockMeshDictInitial Conditionstransport PropertiescontrolDictfvSchemesfvSolutionRunning OpenFOAM

[302.044] – Univ. Assist. MSc. Francesco Romanò 2/32


OpenFOAMDescription of the Software

OpenFOAM: Description of the Software

. The OpenFOAM CFD Toolbox is a free, open source CFDsoftware package which solves using a collocation FVM;

. It can solve complex fluid flows involving chemicalreactions, turbulence and heat transfer, solid dynamicsand electromagnetics and includes tools for meshing, pre-and post-processing;

. Almost everything runs in parallel as standard;

. OpenFOAM offers users possibility to customise and extendthe existing functionality.



























OpenFOAMblockMeshDict

OpenFOAM: blockMeshDict

. <problem_folder>/constant/polyMesh/blockMeshDict

◦ initial banner:/*--------------------------------*- C++ -*----------------------------------*\| ========= | || \\ / F ield | OpenFOAM: The Open Source CFD Toolbox || \\ / O peration | Version: 2.2.2 || \\ / A nd | Web: www.OpenFOAM.org || \\/ M anipulation | |\*---------------------------------------------------------------------------*/

◦ FoamFile: sub-dictionary delimited by curly bracketscontaining code’s information:

FoamFile{

version 2.0;format ascii;class dictionary;object blockMeshDict;

}// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //






◦ scaling parameter:

convertToMeters 0.1;

◦ vertices: function delimited by parenthesis specifyingCartesian coordinates of the domain vertices1:

vertices(

(0 0 0)(1 0 0)

...(1 1 0.1)(0 1 0.1)

);1For 2–D cases, it is necessary to indicate suitable BCs.






◦ blocks: function specifying how many mesh blocks formthe 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 firstand the last element of the mesh blockis setted 1 for each direction: it meansit is used a constant discretization inx, y (“and z”).

blocks(

hex(0 1 2 3 4 5 6 7)(20 20 1)simpleGrading(1 1 1));






◦ 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 thiscase between nodes 0 and 5, and passing throughthe point in parenthesis).

edges(

arc 0 5 (0.469846 0.17101 0));




OpenFOAM: blockMeshDict. <problem_folder>/constant/polyMesh/blockMeshDict

◦ boundary: function specifying name, type and facesof each sub-bound. They are delimitedby curly brackets after each of their name.

boundary(<NameOfTheBoundary>{

type <TypeOfTheBoundary>;faces(

(<4EdgesOfTheCurrentFace>));

});






◦ type: type of the boundary that can be wall, empty,patch, etc...

◦ mergePatchPairs: tool that defines a list of patches tobe meshed using a reciprocal corre-spondence of master and slave.

mergePatchPairs();// ***************************************** //

◦ running commands:<problem\_folder>$ blockMesh



OpenFOAMInitial Conditions

OpenFOAM: Initial Conditions

. <problem_folder>/0/p



FoamFile{

version 2.0;format ascii;class volScalarField;object p;

}// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //






◦ dimensions of the system:dimensions [0 2 -2 0 0 0 0]; % m^2/s^2

◦ internalField: it can be uniform (only one value) ornot (scalar point-wise field)

internalField uniform 0;






◦ boundaryField: function containing boundary condi-tions referred to the name already usedcreating the mesh.

boundaryField{<NameOfTheBoundary>{

type <TypeOfTheBoundaryCondition>;}}// ***************************************** //

◦ type: type of the boundary condition that can bezeroGradient, fixedValue, empty, etc...





. <problem_folder>/0/U



FoamFile{

version 2.0;format ascii;class volVectorField;object U;

}// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //






◦ dimensions of the system:dimensions [0 1 -1 0 0 0 0]; % m/s

◦ internalField: it can be uniform (only one vectorialvalue) or not (vectorial point-wise field)

internalField uniform (0 0 0);






◦ boundaryField: function containing boundary condi-tions referred to the name already usedcreating the mesh.

boundaryField{<NameOfTheBoundary>{

type <TypeOfTheBoundaryCondition>;}}// ***************************************** //

◦ type: type of the boundary condition that can bezeroGradient, fixedValue, empty, etc...



OpenFOAMtransportProperties

OpenFOAM: transportProperties

. <problem_folder>/constant/transportProperties



FoamFile{

version 2.0;format ascii;class dictionary;location "constant"object transportProperties;

}// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



OpenFOAMtransportProperties

OpenFOAM: transportProperties

. <problem_folder>/constant/transportProperties

◦ physical properties of the system2:

nu nu [ 0 2 -1 0 0 0 0 ] 0.01; % m^2/s

// **************************************** //

2In the case of incompressible single-phase flows, just kinematicviscosity has to be defined. Other properties should be eventuallyincluded in the transportProperties dictionary.



OpenFOAMcontrolDict

OpenFOAM: controlDict

. <problem_folder>/system/controlDict



FoamFile{

version 2.0;format ascii;class dictionary;location "system";object controlDict;

}// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



OpenFOAMcontrolDict



◦ application: function that defines the model to use.

application icoFoam;

◦ startFrom: command used to set the initial time of thesimulation. In this case the command isstarTime and, in the next row, it indicatesthat the simulation has tin = 0. The initialcondition is then in a directory named 0.To use a previous calculation, instead of thecommand startTime, latestTime is used.

startFrom startTime;startTime 0;



OpenFOAMcontrolDict

OpenFOAM: controlDict. <problem_folder>/system/controlDict

◦ stopAt: command used to set the final time of the simu-lation. In this case the command is endTimeand indicates that the simulation has tfin = .5.

stopAt endTime;endTime 0.5;

◦ deltaT: defines the time step used for the simulation.Numerical stability problems can be due to timeand the spatial discretization steps. Theoretical-ly analysing the incompressible flow solver,the stability is controlled by the local Courantnumber, which has to be less than one.

deltaT 0.005;



OpenFOAMcontrolDict

OpenFOAM: controlDict. <problem_folder>/system/controlDict

◦ writeControl: defines the kind of control used to savedata. The command timeStep saveseach (writeInterval)x(time steps).The storage is in folders created usingas name the time of saving.

◦ purgeWrite: defines a limit on the number of storage di-rectories: if the needed directories are morethan the indicator, the previous data arecyclically overwritten. Not to define a limitpurgeWrite has to be 0.

writeControl timeStep;writeInterval 20;purgeWrite 0;



OpenFOAMcontrolDict



◦ further instruction for saving the data:

writeFormat ascii;writePrecision 6;writeCompression off;timeFormat general;timePrecision 6;runTimeModifiable true;

// ***************************************** //



OpenFOAMfvSchemes

OpenFOAM: fvSchemes

. <problem_folder>/system/fvSchemes



FoamFile{

version 2.0;format ascii;class dictionary;location "system";object fvSchemes;

}// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



OpenFOAMfvSchemes

OpenFOAM: fvSchemes


◦ ddtSchemes: contains the information about the methodto discretize the temporal derivative.Euler means that the time derivative isdiscretized using an Implicit Euler scheme.Other options are: CrankNicholson,backward, etc...

ddtSchemes{

default Euler;}



OpenFOAMfvSchemes

OpenFOAM: fvSchemes


◦ gradSchemes: contains the information about theselected method to discretize the gradient.Gauss linear means that OpenFOAMdiscretizes the gradient operator with thelinear Gaussian method. Another methodis the least squares method settingleastSquares instead of Gauss linear.

gradSchemes{

default Gauss linear;grad(p) Gauss linear;

}



OpenFOAMfvSchemes

OpenFOAM: fvSchemes. <problem_folder>/system/fvSchemes

◦ divSchemes and laplacianSchemes:contains information about the selected method fordiscretizing the divergence and laplacian operators.

divSchemes{

default none;div(phi,U) Gauss linear;

}laplacianSchemes{

default none;laplacian(nu,U) Gauss linear orthogonal;laplacian((1|A(U)),p) Gauss linear orthogonal;

}[302.044] – Univ. Assist. MSc. Francesco Romanò 26/32


OpenFOAMfvSchemes

OpenFOAM: fvSchemes


◦ interpolationSchemes: sets the interpolation method.

interpolationSchemes{

default linear;interpolate(HbyA) linear;

}

◦ snGradSchemes: sets the treatment for (·),n.

snGradSchemes{

default orthogonal;}



OpenFOAMfvSchemes

OpenFOAM: fvSchemes


◦ fluxRequired: sets the information about fields forwhich is required to calculate a flux.

fluxRequired{

default no;p ;

}// *************************************** //



OpenFOAMfvSolution

OpenFOAM: fvSolution

. <problem_folder>/system/fvSolution



FoamFile{

version 2.0;format ascii;class dictionary;location "system";object fvSolution;

}// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



OpenFOAMfvSolution



◦ solvers: defines the set-up of the linear solvers.

solvers{

<Var>{

solver <SolverType>;preconditioner <PreconditionerType>;tolerance <AbsoluteTollerance>;relTol <RelativeTollerance>;

}}



OpenFOAMfvSolution



◦ <SplittingOperator>: defines the respective treatmentof pressure and velocity.

PISO{

nCorrectors 2;nNonOrthogonalCorrectors 0;pRefCell 0;pRefValue 0;

}// **************************************** //



OpenFOAMRunning a Case

OpenFOAM: Running 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


Documents

[302.044] Numerical Methods in Fluid Dynamics …info.tuwien.ac.at/ViennaOpenFOAMUserGroup/9thb... · OpenFOAM Tutorial Finite Volume Method, Dictionary ... [email protected]