[efirvida]

Hi foamers!!
I have a question about relaxation factor and the accuracy of the solution.
I'm running a 2D flow over a square cylinder case, for differents Reynolds numbers. The things Is that I have tested the same case for different configurations, and relaxations factor, and the result in some cases are very far from each other, so I don't know how to set the correct one.

the attachment shows a different plots derived from my simulations to clarify my question

[simrego]

Hi!


Have you reached the convergence in all cases? And what is simulation time? simpleFoam is a steady-state solver, you have no time there. The time in simpleFoam is just like an iteration step towards your solution, it's not a real time. With smaller relaxation factors you will need more iterations since if you should step 1 towards your solution, you step only 0.8 (with 0.8 relax factor. It's not that simple but something like that.)
With different schemes you can get a bit different results especially in physically complex cases, but i think this is too much.
What was the convergence criteria in the cases? You also monitored the drag coefficient, or just stopped after the residuals became "small"?

[efirvida]

Originally Posted by simrego

Hi!
Have you reached the convergence in all cases? And what is simulation time? simpleFoam is a steady-state solver, you have no time there. The time in simpleFoam is just like an iteration step towards your solution, it's not a real time. With smaller relaxation factors you will need more iterations since if you should step 1 towards your solution, you step only 0.8 (with 0.8 relax factor. It's not that simple but something like that.)
With different schemes you can get a bit different results especially in physically complex cases, but i think this is too much.
What was the convergence criteria in the cases? You also monitored the drag coefficient, or just stopped after the residuals became "small"?

Hi first of all thanks for your attention, maybe I have to be more clear on my question. The simulation time on this plots was only for test the computational cost of each simulation, all the cases were running for 3000 iterations because they never converge criteria. my residuals always stay on a oscillatory state like I show in this pic:



and the drag coefficien lice this:


and my fvSolution file is:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.1                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver                  GAMG;
        smoother                DICGaussSeidel;
        cacheAgglomeration      true;
        nCellsInCoarsestLevel   500;
        nPreSweeps              1;
        nPostSweeps             2;
        nFinestSweeps           2;
        agglomerator            faceAreaPair;
        mergeLevels             2;
        tolerance               1e-012;
        relTol                  0;
    }

    pFinal
    {
        $p;
        tolerance       1e-06;
        relTol          0;
    }

    U
    {
        type            coupled;
        solver          PBiCCCG;
        preconditioner  DILU;
        tolerance       (1e-05 1e-05 1e-05);
        relTol          (0 0 0);
    }

    "(k|epsilon|omega)"
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance       1e-05;
        relTol          0;
    }
}

SIMPLE
{
    nNonOrthogonalCorrectors  1;
    residualControl
    {
        p                     1e-5;
        U                     1e-5;
        "(k|epsilon|omega)"   1e-5;
    } 
}

relaxationFactors
{
    
    fields
    {
        p              <variable>;
    }
    equations
    {
        U              <variable>;
        ".*"           <variable>;
    }
}   

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