[Werne]

Hey,

I'm getting some strange results for the residuals of my simulation. For the first 2000 iterations it looks ads if the simulation will converge. However, afterwards I'm getting strange "jumps" in the values of the residuals, as you can see in the attached plot.

I didn't change any files or values during the simulation.

Does anybody know what could be source of this behaviour?
I'm using rhoSimpleFoam with the following fvSchemes and fvSolution files:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default    bounded Gauss upwind;
    div(phi,U)      bounded Gauss upwind;
    div((muEff*dev2(T(grad(U))))) Gauss linear;
    div(phi,e)      bounded Gauss upwind;
    div(phi,omega) bounded Gauss upwind;  
    div(phi,k)      bounded Gauss upwind;
    div(phi,Ekp)    bounded Gauss upwind;
}

laplacianSchemes
{
    default      Gauss linear corrected;
    laplacian(muEff,U) Gauss linear corrected;
    laplacian(alphaEff,e) Gauss linear corrected;
    laplacian((rho*(1|A(U))),p) Gauss linear corrected;
    laplacian(DomegaEff,omega) Gauss linear corrected;  
    laplacian(DkEff,k) Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p               ;
}

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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
 

   p
    {
        solver          GAMG;
        tolerance       1e-08;
        relTol          0.05;
        smoother        GaussSeidel;
        cacheAgglomeration off;
        nCellsInCoarsestLevel 20;
        agglomerator    faceAreaPair;
        mergeLevels     1;
    }

    U
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        nSweeps         2;
        tolerance       1e-08;
        relTol          0.1;
    }

    e
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-08;
        relTol          0.1;
    }

    "(k|omega)" 
    {
        $U;
        tolerance       1e-09;
        relTol          0.1;
    }    
 
}

SIMPLE
{
    nNonOrthogonalCorrectors 2;
    rhoMin          rhoMin [ 1 -3 0 0 0 ] 0.5;
    rhoMax          rhoMax [ 1 -3 0 0 0 ] 10;

    residualControl
    {
        p               1e-8;        
        U               1e-8;        
        e               1e-8;        

        // possibly check turbulence fields
           "(k|epsilon|omega)" 1e-8;    
    }
}

relaxationFactors
{
    fields
    {
        p               0.1; //0.1
        rho             0.05; //0.05
    }
    equations
    {
        U               0.7; //0.7
        k        0.7; //0.7
        omega        0.7; //0.7
        e               0.7; //0.7
    }
}

[jherb]

This is probably caused because the solution of the omega/U equation reaches (is lower than) the absolute limit of the solver set in system/fvSolution, something like

        tolerance       1e-09;

If you want lower residuals, you have to decrease this value.

[Werne]

Thank you, decreasing the tolerance solved my problem!

edit: No, it didn't, it just delayed it a bit. Although I decreased the tolerance to 1e-9 it still happened.