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-   -   Problems with an unsteady problem (http://www.cfd-online.com/Forums/openfoam/99280-problems-unsteady-problem.html)

samiam1000 March 30, 2012 08:44

Problems with an unsteady problem
 
Dear All,

I am running buoyantPimpleFoam to study an unsteady case, of course. I want to simulate the transient of the temperature inside a room, when I am cooling it down.

I have a complex mesh (I got it from Fluent) and I have both a structured and an unstructured mesh.
The point is that it works only if I choose these solvers:
Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.1.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    "rho.*"
    {
        solver                        GAMG;
        preconditioner                GAMG;
        mergeLevels                1;
        smoother                GaussSeidel;
        agglomerator                faceAreaPair;
        nCellsInCoarsestLevel        100;
        tolerance                1e-08;
        relTol                        0.01;
    }

    p_rgh
    {
        solver                        GAMG;
        preconditioner                GAMG;
        mergeLevels                1;
        smoother                GaussSeidel;
        agglomerator                faceAreaPair;
        nCellsInCoarsestLevel        100;
        tolerance                1e-08;
        relTol                        0.01;
    }

    p_rghFinal
    {
        $p_rgh;
        relTol          0;
    }

    "(U|h|k|epsilon|R)"
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance      1e-09;
        relTol          0.01;
        /*solver                smoothSolver;
        smoother        GaussSeidel;
        tolerance        1e-08;
        relTol                0.01;
            nSweeps                1;*/
        /*solver                        GAMG;
        preconditioner                GAMG;
        mergeLevels                6;
        smoother                GaussSeidel;
        agglomerator                faceAreaPair;
        nCellsInCoarsestLevel        100;
        tolerance                1e-08;
        relTol                        0.01;*/
    }

    "(U|h|k|epsilon|R)Final"
    {
        $U;
        relTol          0;
    }
}

PIMPLE
{
    momentumPredictor yes;
    nOuterCorrectors 2;
    nCorrectors    3;
    nNonOrthogonalCorrectors 2;
}


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

On the contrary, if I try to use either GAMG or smoothSolver I have a very strange behaviour at the interface (I mean where there is the transition between the structured and the unstructured mesh): the velocity increase (as if there is a source).
Do you know why this happens?
You can und that it is a very problem, since the solution should not depend on the solver I choose.

Any idea?

Thanks,

Samuele

sachin April 5, 2012 03:49

Hi Samuele..
Did you check changing value for nNonOrthogonalCorrectors...
Perhaps the solvers would be sensitive to this value...Just a passing thought ...

Best Luck
Sachin


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