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-   -   realizableKE hanging and then exploding (http://www.cfd-online.com/Forums/openfoam-solving/87380-realizableke-hanging-then-exploding.html)

vaina74 April 19, 2011 01:49

realizableKE hanging and then exploding
 
Hi foamers,

I have some problems with the k-epsilon realizable turbulent model. I already used it for other cases without troubles, so I'm not able to understand what's wrong or what I can improve.

The simulation starts bad, hanging for several minutes, but then it seems to run:
Code:

Time = 1

smoothSolver:  Solving for Ux, Initial residual = 0.470174, Final residual = 0.00400859, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 1, Final residual = 0.00600497, No Iterations 4
smoothSolver:  Solving for Uz, Initial residual = 1, Final residual = 0.00335194, No Iterations 4
GAMG:  Solving for p, Initial residual = 1, Final residual = 2.767, No Iterations 1000
time step continuity errors : sum local = 0.00166243, global = 9.18302e-06, cumulative = 9.18302e-06
smoothSolver:  Solving for epsilon, Initial residual = 0.000497916, Final residual = 1.88216e-06, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 1, Final residual = 0.00867952, No Iterations 4
ExecutionTime = 751.02 s  ClockTime = 751 s

Anyway, after some hundreds iterations, the computation explode:
Code:

Time = 398

smoothSolver:  Solving for Ux, Initial residual = 0.288734, Final residual = 0.000692462, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.288723, Final residual = 0.00069192, No Iterations 4
smoothSolver:  Solving for Uz, Initial residual = 0.288259, Final residual = 0.000668387, No Iterations 4
GAMG:  Solving for p, Initial residual = 2.92554e-10, Final residual = 2.92554e-10, No Iterations 0
time step continuity errors : sum local = 5.31272e+87, global = -2.8754e+74, cumulative = -1.25563e+76
smoothSolver:  Solving for epsilon, Initial residual = 0.0914353, Final residual = 8.60873e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 6.30816e-14, Final residual = 6.30816e-14, No Iterations 0
ExecutionTime = 7035.03 s  ClockTime = 7035 s

GGI pair (stitch_in, stitch_out) : 1.71408e+78 1.71091e+78 Diff = 7.54614e+74 or 0.0440244 %
Cyclic GGI pair (cyclic_1, cyclic_2) : 9.55415e+76 9.5507e+76 Diff = -1.62343e+73 or 0.0169919 %
Cyclic GGI pair (symmetry_1, symmetry_2) : 6.86082e+76 6.86082e+76 Diff = 1.06058e+62 or 1.54585e-13 %

I think I can edit something in fvSolution (or fvSchemes?), but I don't know how. Any suggestion? I report both files.

fvSolution
Code:

solvers
{
    p GAMG
    {
        tolerance            1e-8;
        relTol                0.01;
        smoother              GaussSeidel;
        cacheAgglomeration    true;
        nCellsInCoarsestLevel 20;
        agglomerator          faceAreaPair;
        mergeLevels          1;
    };

    U smoothSolver
    {
        smoother              GaussSeidel;
        nSweeps              2;
        tolerance            1e-7;
        relTol                0.01;
    };

    k smoothSolver
    {
        smoother              GaussSeidel;
        nSweeps              2;
        tolerance            1e-7;
        relTol                0.01;
    };

    epsilon smoothSolver
    {
        smoother              GaussSeidel;
        nSweeps              2;
        tolerance            1e-7;
        relTol                0.01;
    };
}

SIMPLE
{
    nNonOrthogonalCorrectors  0;
    pRefCell                  0;
    pRefValue                0;
}

relaxationFactors
{
    p                              0.3;
    U                            0.5;
    k                        0.5;
    epsilon                  0.5;
}

fvSchemes
Code:

ddtSchemes
{
    default                      steadyState;
}

gradSchemes
{
    default                      faceMDLimited Gauss linear 0.5;
}

divSchemes
{
    default                      none;
    div(phi,U)                    Gauss GammaV 0.2;
    div(phi,k)                    Gauss upwind;
    div(phi,epsilon)              Gauss upwind;
    div(phi,tau)                  Gauss limitedLinear 1;
    div(phi,omega)                Gauss upwind;
    div(phi,nuTilda)              Gauss limitedLinear 1;
    div((nuEff*dev(grad(U).T()))) Gauss linear;
}

laplacianSchemes
{
    default                      Gauss linear limited 0.5;
    laplacian(DomegaEff,omega)    Gauss linear limited 0.33;
//    laplacian(DepsilonEff,epsilon) Gauss linear corrected;
}

interpolationSchemes
{
    default                      linear;
}

snGradSchemes
{
    default                      limited 0.6;
}

fluxRequired
{
    default                      no;
    p;
}


openfoam_user April 19, 2011 05:48

Hi,

I have used realizableKE turbulence model for external aerodynamics with the following settings.

fvSchemes:

ddtSchemes
{
default steadyState;
}

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

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

laplacianSchemes
{
default Gauss linear corrected;
}

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

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p;
}

fvSolution:
solvers
{
p
{
solver GAMG;
tolerance 1e-7;
relTol 0.1;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration on;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 10;
mergeLevels 1;
};

U
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-5;
relTol 0.1;
};

k
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-5;
relTol 0.1;
};

epsilon
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-5;
relTol 0.1;
};
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
}

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

Best regards,

Stephane.

vaina74 April 20, 2011 05:45

Thank you very much for your help, I'll try to test your fvSolution file.

vaina74 May 2, 2011 09:00

I also tried the fvSchemes and fvSolution settings suggested by Stephane, but I still have bounding epsilon problems - I can see epsilon and evaluated forces getting higher and higher.
Can you explain that? I already used k-epsilon realizable turbulent model without such problems, does it depend on the geometry? I tried to change relaxion factors till 0.2 without success (values get a little lower but always too big). What could I improve in my fvSolution and fvSchemes files?
Thanks for your help, regards.

Zinedine January 10, 2013 09:54

realizableKE problem with OF1.71
 
Hi
I am trying to use Rke turbulence model in a case which runs OK
using standard ke.
Am I missing something when using Rke ?
Has anybody has an example of what needs to be initialise when using Rke please ?
When using ke I initialise k,e,R using standard tools as explained ijn OF user guide etc ?
Do I need to add something elsewhen using Rke please ?

Thanks for your help


Regards

Z.


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