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Porous Media in PimpleFoam - DF coefficients independency

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Old   April 23, 2020, 12:48
Default Porous Media in PimpleFoam - DF coefficients independency
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Luiz Oliveira
Join Date: Aug 2018
Location: Napoli, Italy
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Hello,

I am conducting a simulation of a lateral cavity placed along a riverbank. As vegetation naturally occurs in those regions, I am trying to investigate its effect.
The vegetation is being represented by a momentum drag imposed by a porous media, which is a well accepted simplification. what I realized from my past simulations are that the Ergun coefficients were overestimating the resistance in the porous media (PM). Thus, a hunt begun in order to find the appropriate values. I managed to simulate until the order of 1E-25 for both D and F. Although, it seems that the resistance didn't change along the way, as there were no differences in the velocity curve. It appears that there is no communication between the zones despite the mesh being sharing the same points. I noticed that while the flow stabilizes there is a flux that goes into the porous media although after the stabilization no more energy seems to go into the zone giving U = 0 m/s throughout the domain.
I came with some hypothesis:
  1. LES isn't capable of solving the flow within the porous zone as the eddies are too small;
  2. The natural velocity of the problem is so slow that ridiculous small coefficient is necessary;
  3. Lastly, that there is a misconfiguration in the simulation itself.
fvOptions
Code:
embayment
{
    type            explicitPorositySource;
    active            true;
    selectionMode   cellZone;
    cellZone        embayment;

    explicitPorositySourceCoeffs
    {
        selectionMode   cellZone;
        cellZone        embayment;

        type            DarcyForchheimer;
        
        mu    mu;
        d   (116.62 116.62 4.51E-04);    //Original values d   (116.62 116.62 4.51E-04);
        f   (3.09 3.09 6.08E-03);        //Original values f   (3.09 3.09 6.08E-03);

        coordinateSystem
        {
            origin  (0.25 0.30 0);
            e1      (1 0 0);
            e2      (0 1 0);
        }
    }
}
fvSchemes

Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/

FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object fvSchemes;
}

    ddtSchemes
    {
        default            backward;
    }

    gradSchemes
    {
        default            leastSquares;
    }

    divSchemes
    {
        default         none;
        div(phi,U)      Gauss LUST grad(U);
        div(phi,nuTilda) Gauss linear;
        div((nuEff*dev2(T(grad(U))))) Gauss linear;
        
        div(phi,tracer) Gauss limitedLinear 0 1;
    }

    interpolationSchemes
    {
        default            linear;
    }

    laplacianSchemes
    {
        default         Gauss linear uncorrected;
    }

    snGradSchemes
    {
        default            uncorrected;
    }

    wallDist
    {
        method meshWave;
    }


// ************************************************************************* //
fvSolution
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/

FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object fvSolution;
}
    PIMPLE
    {
        nOuterCorrectors 1;
        nCorrectors     3;
        nNonOrthogonalCorrectors 0;
        pRefCell 0;
        pRefValue 0;
        
        residualControl
        {
            "(p|U)"
            {
                tolerance        1e-06;
                relTol            0;
            }
        }
        
        relaxationFactors
        {
            fields
            {
                p                0.3;
                pFinal            1;
            }
    
            equations
            {
                U                0.7;
                UFinal            1;
                nuTilda            1;
                nuTildaFinal    1;            
            }
        }
    }

    solvers
    {
        p
        {
            solver          GAMG;
            smoother        GaussSeidel;
            tolerance       1e-06;
            relTol          0;
            maxIter         100;
        }
    
        pFinal
        {
            $p;
            smoother        GaussSeidel;
            tolerance       1e-06;
            relTol          0;
        }
    
        U
        {
            solver          PBiCGStab;
            preconditioner  diagonal;
            tolerance       1e-06;
            relTol          0;
              maxIter         100;
        }
    
        UFinal
        {
            $U;
            tolerance       1e-06;
            relTol          0;
        }
        
        tracer
        {
            solver            PBiCGStab;
            preconditioner    diagonal;
            tolerance        1e-06;
            relTol            0;
            minIter            1;
        }
    }

    relaxationFactors
    {
        fields
        {
            p                0.3;
            pFinal            1;
        }
    
        equations
        {
            U                0.7;
            UFinal            1;
            nuTilda            1;
            nuTildaFinal    1;            
        }
    
    }

// ************************************************************************* //
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les, pimplefoam, porous media, transient

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