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Old   November 3, 2011, 08:33
Default No convergence
  #1
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Denis
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Hi,

i'm trying to simulate a 2D flow over an airfoil.
I'm using the simpleFoam with a k-epsilon turbulence model, these are my system files:


fvSolution:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.0.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver          GAMG;
        tolerance       1e-06;
        relTol          0.1;
        smoother        GaussSeidel;
        nPreSweeps      0;
        nPostSweeps     2;
        cacheAgglomeration true;
        nCellsInCoarsestLevel 10;
        agglomerator    faceAreaPair;
        mergeLevels     1;
    }


    U
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-05;
        relTol          0.1;
    }

    k
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-05;
        relTol          0.1;
    }

    epsilon
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-05;
        relTol          0.1;
    }

    
}

SIMPLE
{
    nNonOrthogonalCorrectors 0;
    pRefCell        10;
    pRefValue       0;

    residualControl
    {
        p               1e-6;
        U               1e-6;
        "(k|epsilon|omega)" 1e-3;
    }
}

relaxationFactors
{
    p               0.3;
    U               0.7;
    k               0.7;
    epsilon         0.7;      

// ************************************************************************* //
fvScheme
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.0.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         steadyState;
}

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

divSchemes
{
    default         none;
    div(phi,U)      Gauss upwind;
    div(phi,k)      Gauss upwind;
    div(phi,epsilon) Gauss upwind;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         none;
    laplacian(nuEff,U) Gauss linear corrected;
    laplacian((1|A(U)),p) Gauss linear corrected;
    laplacian(DkEff,k) Gauss linear corrected;
    laplacian(DepsilonEff,epsilon) Gauss linear corrected;
    laplacian(DREff,R) Gauss linear corrected;
    laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
}

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

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p               ;
}


// ************************************************************************* //
The main problem is, there is no convergence especially for the pressure. I get this message:

Code:
#0  Foam::error::printStack(Foam::Ostream&) in "/opt/openfoam201/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#1  Foam::sigFpe::sigHandler(int) in "/opt/openfoam201/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#2  Uninterpreted: 
#3  Foam::PBiCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const in "/opt/openfoam201/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#4  Foam::fvMatrix<double>::solve(Foam::dictionary const&) in "/opt/openfoam201/platforms/linuxGccDPOpt/lib/libfiniteVolume.so"
#5  Foam::fvMatrix<double>::solve() in "/opt/openfoam201/platforms/linuxGccDPOpt/bin/simpleFoam"
#6  Foam::incompressible::RASModels::kEpsilon::correct() in "/opt/openfoam201/platforms/linuxGccDPOpt/lib/libincompressibleRASModels.so"
#7  
 in "/opt/openfoam201/platforms/linuxGccDPOpt/bin/simpleFoam"
#8  __libc_start_main in "/lib/i386-linux-gnu/libc.so.6"
#9  
 in "/opt/openfoam201/platforms/linuxGccDPOpt/bin/simpleFoam"
Gleitkomma-Ausnahme
Has someone an idea how to solve this problem?

Denis
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Old   November 3, 2011, 08:40
Default
  #2
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Bernhard
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It is easier to understand to post a larger part of the log file (before the actual error occurs).

In this case you put relTol to 0.1, which seems high to me. Try to pose a more strict condition on this one.
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Old   November 3, 2011, 09:14
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Denis
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Hi Bernhard,

thank you for your fast response.

So I've changed the tol, maybe you can explain me, what´s the difference between "relTol" and "tolerance".

I attached a plot of the residuals: there you can see a "zig-zacking" of all residuals and you can see that they are "bounded".
Do you have an explanation for that?

Denis
Attached Images
File Type: jpg resiudal.jpg (27.9 KB, 46 views)
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Old   November 21, 2011, 21:20
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HD
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Hi Denis,

I got the same error running simpleFoam, I wonder if you have resolved this issue. If so, could you post the solution?

Thank you!

Best,

Hang
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Old   November 22, 2011, 01:03
Default relTol and tolerance
  #5
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Geon-Hong Kim
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Hi Denis.

Both tolerance and relTol are used for terminating a sub-iteration of each equation.

If the residual reaches tolerance or becomes less than the tolerance you set, then the computation of corresponding equation will be terminated.

If the residual reaches or goes to below than (relTol) x (Initial residual), then the iteration will be terminated as well.

When you set the relTol as 0, then the iteration will be terminated only if the final residual becomes less than the tolerance.

Regards,
Geon-Hong.
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