[tdof]

Hi all,

I'm doing some viscoelastic simulations using viscoelasticFluidFoam in combination with the Leonov model and I'm experiencing a strong checkerboard pattern in the velocity field. Also, the inlet pressure is far too low with a fixed inlet velocity. My experience with viscoelastic fluid simulations is rather limited, I mainly had to focus on getting it to run at all. I can't post the whole model due to a NDA, but I used the standard settings found in the Leonov test case in OpenFOAM Extend 4.0.

I can't post the viscoelasticProperties dict since the settings aren't publicly available, but the relaxation time constant lambda and shear modulus G are known with which I calculated eta_p. There are only sigmafirst and taufirst listed below, but the other ones are identical. I know that it is a niche subject, but maybe someone has experienced similar issues. I was able to find out that the checkerboard problem is linked to the pressure-velocity decoupling and the staggered/collocated grid approach. OF apparently uses a mix of both grid types. Would a different interpolation routine of higher order be able to get rid of this behaviour?

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

libs
(
    "liblduSolvers.so"
      //"libOpenFOAM.so"
      "libsimpleSwakFunctionObjects.so"
      "libswakFunctionObjects.so"
      "libgroovyBC.so"
     );

     
OptimisationSwitches
{
    commsType       nonBlocking;
}     
     
application     viscoelasticFluidFoam;

startFrom       startTime;

startTime       0;

stopAt          endTime;

endTime         5;

deltaT          1e-5;

writeControl    adjustableRunTime;

writeInterval   1;

purgeWrite      0;

writeFormat     ascii;

writePrecision  6;

writeCompression uncompressed;

timeFormat      general;

timePrecision   6;

graphFormat     raw;

runTimeModifiable yes;

adjustTimeStep on;

maxCo          0.8;

maxDeltaT      0.0005;


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

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         Euler;
}

gradSchemes
{
    default         Gauss linear;
    grad(p)         Gauss linear;
    grad(U)         Gauss linear;

}

divSchemes
{
    default                  none;
    div(phi,U)               Gauss upwind;
    div(phi,sigma)           Gauss upwind;
    div(phi,sigmafirst)           Gauss upwind;
    div(phi,sigmasecond)           Gauss upwind;
    div(phi,sigmathird)           Gauss upwind;
    div(phi,sigmafourth)           Gauss upwind;    
    div(tau)                 Gauss linear;
    div(taufirst)                 Gauss linear;
    div(tausecond)                 Gauss linear;
    div(tauthird)                 Gauss linear;
    div(taufourth)                 Gauss linear;
}

laplacianSchemes
{
    default                      none;
    laplacian(etaPEff,U)         Gauss linear corrected;
    laplacian(etaPEff+etaS,U)    Gauss linear corrected;
    laplacian((1|A(U)),p)        Gauss linear corrected;
}

interpolationSchemes
{
    default           linear;
    interpolate(HbyA) linear;
}

snGradSchemes
{
    default         corrected;
}


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

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{

    p
    {
        solver          PCG;
        preconditioner  Cholesky;

        tolerance        1e-07;
        relTol           0;
        minIter          0;
        maxIter          800;
    }

    U
    {

        solver           BiCGStab;
        preconditioner   ILU0;

        tolerance         1e-6;
        relTol            0;
        minIter           0;
        maxIter           1000;
    }

    sigma
    {

        solver           BiCGStab;
        preconditioner   ILU0;

        tolerance         1e-6;
        relTol            0;
        minIter           0;
        maxIter           1000;

    };
    sigmafirst
    {

        solver           BiCGStab;
        preconditioner   ILU0;

        tolerance         1e-6;
        relTol            0;
        minIter           0;
        maxIter           1000;

    };
    sigmasecond
    {

        solver           BiCGStab;
        preconditioner   ILU0;

        tolerance         1e-6;
        relTol            0;
        minIter           0;
        maxIter           1000;

    };
    sigmathird
    {

        solver           BiCGStab;
        preconditioner   ILU0;

        tolerance         1e-6;
        relTol            0;
        minIter           0;
        maxIter           1000;

    };
    sigmafourth
    {

        solver           BiCGStab;
        preconditioner   ILU0;

        tolerance         1e-6;
        relTol            0;
        minIter           0;
        maxIter           1000;

    };    
}

PISO
{
    nCorrectors    2;
    nNonOrthogonalCorrectors 2;
    pRefCell        0;
    pRefValue       0;
}

relaxationFactors
{
    p               0.2;
    U               0.2;
    tau             0.2;
}


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

FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }
    fixedWalls
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value           uniform 0;
    }

}


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

FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform (0.009279 0 0);
    }
    
    
    
    
    fixedWalls
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    outlet
    {
        type            zeroGradient;
    }

}


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

FoamFile
{
    version     2.0;
    format      ascii;
    class       volSymmTensorField;
    object      sigmafirst;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [1 -1 -2 0 0 0 0];

internalField   uniform (50 0 0 50 0 50);

boundaryField
{
    inlet
    {
        //type            fixedValue;
        //value           uniform (0 0 0 0 0 0);
        type            zeroGradient;
    }
    fixedWalls
    {
        type            zeroGradient;
    }
    outlet
    {
        type            zeroGradient;
    }

}


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

FoamFile
{
    version     2.0;
    format      ascii;
    class       volSymmTensorField;
    object      tau;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [1 -1 -2 0 0 0 0];

internalField   uniform (0 0 0 0 0 0);

boundaryField
{
    inlet
    {
        //type            fixedValue;
        //value           uniform (0 0 0 0 0 0);
        type            zeroGradient;
    }
    fixedWalls
    {
        type            zeroGradient;
    }
    outlet
    {
        type            zeroGradient;
    }

}


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