[nikovasi]

Hi guys,

I'm trying to solve the steady-state laminar compresible Poiseuille flow through a 2D channel using rhoSimpleFoam.

The rhoSimpleFoam solver converges and for the most part the solution looks reasonable as seen in the attached images. However, taking a closer look at the outlet, a weird behaviour is seen for the pressure.

I have tried using a finer mesh and also played around with fvSchemes and fvSolution controls but this behaviour persists and even becomes worse in some cases.

I have also tried rhoPimpleFoam. In that case, when steady-state is reached, I don't get the exact same behaviour seen with rhoSimpleFoam but the pressure shows a "wavy" profile near the outlet.

Since this is a pretty simple case I expect that someone else has encountered something similar? Any help will be greatly appreciated. Thanks!


blockMeshDict

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.7.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/

FoamFile
{
    version         2.0;
    format          ascii;

    root            "";
    case            "";
    instance        "";
    local           "";

    class           dictionary;
    object          blockMeshDict;
}

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

scale 1e0;


vertices
(
    (0      0     0)
    (2e-5   0     0)
    (2e-5   5e-7  0)
    (0      5e-7  0)
    (0      0     5e-8)
    (2e-5   0     5e-8)
    (2e-5   5e-7  5e-8)
    (0      5e-7  5e-8)
);

blocks
(
hex (0 1 2 3 4 5 6 7) dsmcZone (1000 50 1) simpleGrading (1 1 1)
);

boundary
(

    inlet
    {
        type patch;
        faces 
        (
        (0 4 7 3)
        );
    }

    outlet
    {
        type patch;
        faces 
        (
        (1 2 6 5)
        );
    }
    wall
    {
        type wall;
        faces
        (
        (7 6 2 3)
        );   
    }    
    symmetry
    {
        type symmetryPlane;
        faces
        (
        (4 5 1 0)
        );   
    }
    empty
    {
        type empty;
        faces 
        (
        (4 5 6 7)
        (0 3 2 1)
        );
    }
    
);

mergePatchPairs
(
);


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

thermoProperties

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      thermophysicalProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

thermoType
{
    type             hePsiThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectGas;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        molWeight   39.93;
    }
    thermodynamics
    {
        Cp         520.33;
        Hf          0;
    }
    transport
    {
        mu         2.117e-5;
        Pr          0.666667;
    }
}


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

p

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2206                                  |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    arch        "LSB;label=32;scalar=64";
    class       volScalarField;
    location    "0";
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 20000;


boundaryField
{
    inlet
    {
        type            totalPressure;
        gamma           1.66667;
        p0              uniform 100000;
        value           uniform 100000;
    }
    outlet
    {
        type            fixedValue;
        value           uniform 20000;
    }
    wall
    {
        type            zeroGradient;
    }
    symmetry
    {
        type            symmetryPlane;
    }
    empty
    {
        type            empty;
    }
}

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

T

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2206                                  |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    arch        "LSB;label=32;scalar=64";
    class       volScalarField;
    location    "0";
    object      T;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 1 0 0 0];

internalField   uniform 300;

boundaryField
{
    inlet
    {
        type            totalTemperature;
        gamma           1.66667;
        T0              uniform 300;
        value           uniform 300;
    }
    outlet
    {
        type            zeroGradient;
    }
    wall
    {
        type            fixedValue;
        value           uniform 300;
    }
    symmetry
    {
        type            symmetryPlane;
    }
    empty
    {
        type            empty;
    }
}

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

U

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2206                                  |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    arch        "LSB;label=32;scalar=64";
    class       volVectorField;
    location    "0";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{
    inlet
    {
        type            pressureInletVelocity;
        value           uniform (0 0 0);
    }
    outlet
    {
        type            zeroGradient;
    }
    wall
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    symmetry
    {
        type            symmetryPlane;
    }
    empty
    {
        type            empty;
    }
}

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

fvSchemes

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2206                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         Gauss linear;

    div(((rho*nuEff)*dev2(T(grad(U)))))      Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

wallDist
{
    method meshWave;
}

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

fvSolution

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2206                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver          GAMG;
        smoother        GaussSeidel;
        nSweeps         2;
        tolerance       1e-06;
        relTol          0.0;
        minIter         3;
        maxIter         100;
        nCellsInCoarsestLevel 100;
    }

    "(U|e)"
    {
        solver          PBiCGStab;
        preconditioner  DILU;
        minIter         3;
        maxIter         100;
        tolerance       1e-8;
        relTol          0.0;
    }

}

SIMPLE
{

    momentumPredictor           yes;
    transonic                   yes;
    nNonOrthogonalCorrectors    1;
    turbOnFinalIterOnly         false;

    residualControl
    {
        p       1e-5;
        U       1e-7;
        e       1e-6;
    }    

}

relaxationFactors
{
    equations
    {
        p       0.3;
        U       0.7;
        e       0.7;
    }
}

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