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pressure and velocity in OpenFoam is smaller than Fluent

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Old   September 18, 2013, 05:32
Default how I can increase the accuracy of pressure ?
  #1
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Hi all
I have simulated flow around a cylinder by OF and FLUENT
In both software, I use a high quality and fine structure mesh which lead to y+<5 over walls and use Kw-sst model

also the setting for OF and FLUENT is as follow

FLUENT BCs:
inlet ========> velocity inlet U=7m/sec k=.2 omega=170
outlet=======> pressure outlet
FLUENT settigs
solver =============> PISO
residual=1e-5


In OF I have used pimpleFoam and setting are as follow

any help will be appreciated


Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM Extend Project: Open source CFD        |
|  \\    /   O peration     | Version:  1.6-ext                               |
|   \\  /    A nd           | Web:      www.extend-project.de                 |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      k;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0.2;

boundaryField
{
    wallup
    {
        type            kLowReWallFunction;
        value           uniform .2;
    }

    outlet
    {
        type            inletOutlet;
        inletValue      uniform .2;
        value           uniform .2;
    }
    inlet
    {
        type            turbulentIntensityKineticEnergyInlet;
        intensity       0.02;
        value           uniform .2;
    }
    circle
    {
        type            kLowReWallFunction;
        value           uniform .2;
    }
    frontAndBackPlanes
    {
        type            empty;
    }
}


// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM Extend Project: Open source CFD        |
|  \\    /   O peration     | Version:  1.6-ext                               |
|   \\  /    A nd           | Web:      www.extend-project.de                 |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    location    "0";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform ( 0 0 0 );

boundaryField
{

    wallup
    {
        type            fixedValue;
        value           uniform ( 0 0 0 );
    }

    circle
    {
        type            fixedValue;
        value           uniform ( 0 0 0 );
    }

    inlet
    {
        type            fixedValue;
        value           uniform ( 7. 0 0 );
    }
    outlet
    {
        type            inletOutlet;
        inletValue      uniform ( 0 0 0 );
        value           uniform ( 0 0 0 );
    }
    frontAndBackPlanes
    {
        type            empty;
    }
}


// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM Extend Project: Open source CFD        |
|  \\    /   O peration     | Version:  1.6-ext                               |
|   \\  /    A nd           | Web:      www.extend-project.de                 |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{

    wallup
    {
        type            zeroGradient;
    }
 
    circle
    {
        type            zeroGradient;
    }

    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value           uniform 0;
    }
    frontAndBackPlanes
    {
        type            empty;
    }
}


// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM Extend Project: Open source CFD        |
|  \\    /   O peration     | Version:  1.6-ext                               |
|   \\  /    A nd           | Web:      www.extend-project.de                 |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      omega;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 170;

boundaryField
{
    wallup
    {
        type            omegaWallFunction;
        value           uniform 170;
    }
    wallp
    {
        type            omegaWallFunction;
        value           uniform 170;
    }
    outlet
    {
        type            inletOutlet;
        inletValue      uniform 170;
        value           uniform 170;
    }
    inlet
    {
        type            turbulentMixingLengthFrequencyInlet;
        mixingLength    0.005;
        phi             phi;
        k               k;
        value           uniform 170;
    }
    plate
    {
        type            omegaWallFunction;
        value           uniform 170;
    }
    circle
    {
        type            omegaWallFunction;
        value           uniform 170;
    }
    frontAndBackPlanes
    {
        type            empty;
    }
}


// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM Extend Project: Open source CFD        |
|  \\    /   O peration     | Version:  1.6-ext                               |
|   \\  /    A nd           | Web:      www.extend-project.de                 |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{
    wallup
    {
        type            nutUSpaldingWallFunction;
        value           uniform 0;
    }
    wallp
    {
        type            nutUSpaldingWallFunction;
        value           uniform 0;
    }
    outlet
    {
        type            calculated;
        value           uniform 0;
    }
    inlet
    {
        type            calculated;
        value           uniform 0;
    }
    plate
    {
        type            nutUSpaldingWallFunction;
        value           uniform 0;
    }
    circle
    {
        type            nutUSpaldingWallFunction;
        value           uniform 0;
    }
    frontAndBackPlanes
    {
        type            empty;
    }
}


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

Last edited by mechy; September 20, 2013 at 16:24.
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Old   September 18, 2013, 08:56
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  #2
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Andre Weiner
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Hello!

I don't have OF 1.6-ext installed, so i it's difficult to know what the bc's for k, omega and nut do.
In your case (simple geometry) i would just set the following settings :
k - zeroGradient
omega - an automatic wallfunction like here
nut - 0 or calculated

Also note that the implementation of k-omega-sst may not be the same as there are various types of source terms (for example for near-wall treatment).

How do you control the residuals (fvSolution file)?

Hope i could help!

Best regards
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Old   September 18, 2013, 10:11
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  #3
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Hi
thanks for reply
I use the OF 2.2 not 1.6-ext (only the header have 1.6)
also my fvScheme an fvSolution are :


Code:
/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.3                                   |
|   \\  /    A nd           | Web:      http://www.openfoam.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version         2.0;
    format          ascii;
    class           dictionary;
    object          fvSolution;
}

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

solvers
{
    p
    {
        solver           GAMG;
        tolerance        1e-5;
        relTol           .0;
        smoother         GaussSeidel;
        nPreSweeps       1;
        nPostSweeps      2;
        cacheAgglomeration true;
        directSolveCoarsest true;
        agglomerator     faceAreaPair;
        nCellsInCoarsestLevel 20;
        mergeLevels      1;
        minIter          1;
    }
    pFinal
    {
        solver           GAMG;
        tolerance        1e-8;
        relTol           0;
        smoother         GaussSeidel;
        nPreSweeps       1;
        nPostSweeps      2;
        cacheAgglomeration true;
        agglomerator     faceAreaPair;
        nCellsInCoarsestLevel 20;
        mergeLevels      1;
        minIter          1;
    }

    "(U|k|omega)"
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance        1e-5;
        relTol           0;
        nSweeps          1;     
        minIter          1;
    }
    "(UFinal|kFinal|omegaFinal)"
    {

        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-6;
        relTol           0.0;
        nSweeps          1;   
        minIter          1;
    }
}

PIMPLE
{
    nOuterCorrectors    10;
    nCorrectors         2;
    nNonOrthogonalCorrectors 3;

    pRefCell            0;
    pRefValue           0;
//    momentumPredictor yes;
    ddtPhiCorr no;
    correctPhi no;

}


relaxationFactors
{
    fields
    {
        p               0.3;
    }
    equations
    {
        U               0.7;
        k               0.7;
        omega           0.7;
    }
}
cache
{
    grad(U);
}

// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default Euler;
}

gradSchemes
{
    default           Gauss linear ;
}

divSchemes
{
    default         none;
    div(phi,U)      Gauss limitedLinearV 1;
    div(phi,k)      Gauss limitedLinear 1;
    div(phi,omega)  Gauss limitedLinear 1;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
     div((nuEff*dev(grad(U).T())))  Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p;
}
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Old   September 18, 2013, 11:37
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  #4
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Andre Weiner
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Have you tried to run the simulation in pure PISO mode?
It shouldn't make any difference but i think it's worth a try.

How much is the difference between the results?
Do the fields look similar in both simulations?
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Old   September 18, 2013, 16:19
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the flow field in both of them, are similar
but the value of pressure has a about 10% difference
the min p in OF about 10 pa greater than FLUENT
for example if p in OF = -50 in FLUent minp=-60
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