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Problems with an unsteady problem

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Old   March 30, 2012, 08:44
Default Problems with an unsteady problem
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Samuele Z
Join Date: Oct 2009
Location: Mozzate - Co - Italy
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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
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Old   April 5, 2012, 03:49
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Sachin Kanetkar
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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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