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Description of $ k-\epsilon$ turbulence model

  • Turbulence models and its parameters are set in file turbulenceProperties in directory constant
  • Open e.g.:

    # cat $FOAM_TUTORIALS/incompressible/simpleFoam/pitzDaily/\
    constant/turbulenceProperties

     

    /*--------------------------------*- C++ -*----------------------------------*\
    | =========                 |                                                 |
    | \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |                                                                                                         
    |  \\    /   O peration     | Version:  dev                                   |                                                                                                         
    |   \\  /    A nd           | Web:      www.OpenFOAM.org                      |                                                                                                         
    |    \\/     M anipulation  |                                                 |                                                                                                         
    \*---------------------------------------------------------------------------*/                                                                                                         
    FoamFile                                                                                                                                                                                
    {                                                                                                                                                                                       
        version     2.0;                                                                                                                                                                    
        format      ascii;                                                                                                                                                                  
        class       dictionary;                                                                                                                                                             
        location    "constant";                                                                                                                                                             
        object      turbulenceProperties;                                                                                                                                                   
    }                                                                                                                                                                                       
    // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
    
    simulationType RAS;
    
    RAS
    {
        // Tested with kEpsilon, realizableKE, kOmega, kOmegaSST, v2f,
        // ShihQuadraticKE, LienCubicKE.
        RASModel        kEpsilon;
    
        turbulence      on;
    
        printCoeffs     on;
    }
    
    
    // ************************************************************************* //
    
  • RASModel selects turbulence model
  • kEpsilon means two equation $ k-\epsilon$ model

     

    turbulence      on;
    

     

  • Parameter turbulence can switch turbulence modeling on or off (on/off )

     

    printCoeffs     on;
    

  • Parameter printCoeffs says if model coefficients are printed at start of the computation (on/off )

     

    /*---------------------------------------------------------------------------*\
    | =========                 |                                                 |
    | \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
    |  \\    /   O peration     | Version:  dev                                   |
    |   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
    |    \\/     M anipulation  |                                                 |
    \*---------------------------------------------------------------------------*/
    Build  : dev-e2ccbbbb
    Exec   : simpleFoam
    Date   : Sep 15 2017
    Time   : 11:59:59
    Host   : $HOSTNAME
    PID    : $$
    Case   : $FOAM_RUN/pitzDaily
    nProcs : 1
    sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
    fileModificationChecking : Monitoring run-time modified files using timeStampMaster                                                  
    allowSystemOperations : Disallowing user-supplied system call operations                                                             
                                                                                                                                         
    // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //                                                      
    Create time                                                                                                                          
                                                                                                                                         
    Create mesh for time = 0                                                                                                          
                                                                                                                                         
    Reading field p                                                                                                                      
                                                                                                                                         
    Reading field U                                                                                                                      
                                                                                                                                         
    Reading/calculating face flux field phi                                                                                              
                                                                                                                                         
    Selecting incompressible transport model Newtonian                                                                                   
    Selecting RAS turbulence model kEpsilon                                                                                              
    kEpsilonCoeffs                                                                                                                       
    {                                                                                                                                    
        Cmu             0.09;                                                                                                            
        C1              1.44;                                                                                                            
        C2              1.92;
        C3              0;
        sigmak          1.0;
        sigmaEps        1.3;                                                                                                             
    } 
    
    ...
    

     

  • Parameter kEpsilonCoeffs is optional and can change the default model coefficients in file turbulenceProperties

     

    kEpsilonCoeffs
    {
                Cmu         0.09;
                C1          1.44;
                C2          1.92;
                C3          0;
                sigmak      1.0;
                sigmaEps    1.3;
    }
    
  •