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Sudden jumps in Courant in the middle of the simulation

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Old   May 6, 2014, 07:43
Default Sudden jumps in Courant in the middle of the simulation
  #1
Pj.
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Luca
Join Date: Mar 2013
Posts: 68
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Pj. is on a distinguished road
Hi everybody

I'm running a case with PIMPLE foam with the LES turbulence model.

The problem is that in the middle of the simulation, sudden jumps of several order of magnitude in Courant number appears. Then, strange fact number 2, the simulation converges again

This is the log from pimple foam with the iteration before and after the jump

Code:
Courant Number mean: 0.186631 max: 1.8437
Time = 5.575

PIMPLE: iteration 1
DILUPBiCG:  Solving for Ux, Initial residual = 0.00145738, Final residual = 6.64777e-09, No Iterations 6
DILUPBiCG:  Solving for Uy, Initial residual = 0.0604873, Final residual = 7.45712e-09, No Iterations 9
DILUPBiCG:  Solving for Uz, Initial residual = 0.0274295, Final residual = 8.88052e-09, No Iterations 8
DICPCG:  Solving for p, Initial residual = 0.141566, Final residual = 0.00692174, No Iterations 4
DICPCG:  Solving for p, Initial residual = 0.00791436, Final residual = 0.00037769, No Iterations 16
time step continuity errors : sum local = 7.22241e-08, global = -4.52688e-11, cumulative = -1.72326e-07
DICPCG:  Solving for p, Initial residual = 0.0161718, Final residual = 0.000756972, No Iterations 5
DICPCG:  Solving for p, Initial residual = 0.000876374, Final residual = 4.36954e-05, No Iterations 33
time step continuity errors : sum local = 8.49073e-09, global = -5.75816e-11, cumulative = -1.72383e-07
PIMPLE: iteration 2
DILUPBiCG:  Solving for Ux, Initial residual = 3.12497e-05, Final residual = 8.99954e-09, No Iterations 4
DILUPBiCG:  Solving for Uy, Initial residual = 0.000795909, Final residual = 1.19494e-09, No Iterations 8
DILUPBiCG:  Solving for Uz, Initial residual = 0.00029896, Final residual = 314.057, No Iterations 1001
DICPCG:  Solving for p, Initial residual = 0.999977, Final residual = 0.0263806, No Iterations 3
DICPCG:  Solving for p, Initial residual = 0.0144061, Final residual = 0.000528999, No Iterations 8
time step continuity errors : sum local = 0.00441509, global = 9.945e-09, cumulative = -1.62438e-07
DICPCG:  Solving for p, Initial residual = 0.755181, Final residual = 0.0195148, No Iterations 3
DICPCG:  Solving for p, Initial residual = 0.0397071, Final residual = 9.8571e-07, No Iterations 250
time step continuity errors : sum local = 3.04181e-06, global = 1.62246e-07, cumulative = -1.91817e-10
ExecutionTime = 37649.6 s  ClockTime = 37697 s

Courant Number mean: 2.76008 max: 43683.4
Time = 5.576

PIMPLE: iteration 1
DILUPBiCG:  Solving for Ux, Initial residual = 0.289494, Final residual = 6.77395e-09, No Iterations 14
DILUPBiCG:  Solving for Uy, Initial residual = 0.305659, Final residual = 7.22824e-09, No Iterations 14
DILUPBiCG:  Solving for Uz, Initial residual = 0.316415, Final residual = 9.94743e-09, No Iterations 14
DICPCG:  Solving for p, Initial residual = 0.960833, Final residual = 0.0456337, No Iterations 8
DICPCG:  Solving for p, Initial residual = 0.0100212, Final residual = 0.000488464, No Iterations 49
time step continuity errors : sum local = 0.00244363, global = 1.20192e-05, cumulative = 1.2019e-05
DICPCG:  Solving for p, Initial residual = 0.0416985, Final residual = 0.00189429, No Iterations 10
DICPCG:  Solving for p, Initial residual = 0.00261552, Final residual = 0.000127246, No Iterations 92
time step continuity errors : sum local = 0.000612151, global = 5.09733e-05, cumulative = 6.29923e-05
PIMPLE: iteration 2
DILUPBiCG:  Solving for Ux, Initial residual = 0.242781, Final residual = 2.21545e-09, No Iterations 14
DILUPBiCG:  Solving for Uy, Initial residual = 0.247553, Final residual = 2.30642e-09, No Iterations 14
DILUPBiCG:  Solving for Uz, Initial residual = 0.276608, Final residual = 2.33162e-09, No Iterations 15
DICPCG:  Solving for p, Initial residual = 0.141775, Final residual = 0.0065789, No Iterations 5
DICPCG:  Solving for p, Initial residual = 0.00722017, Final residual = 0.000357133, No Iterations 66
time step continuity errors : sum local = 0.00165265, global = 0.000112039, cumulative = 0.000175032
DICPCG:  Solving for p, Initial residual = 0.0266265, Final residual = 0.00117149, No Iterations 6
DICPCG:  Solving for p, Initial residual = 0.00134573, Final residual = 9.69224e-07, No Iterations 505
time step continuity errors : sum local = 4.90204e-06, global = -6.92753e-09, cumulative = 0.000175025
ExecutionTime = 37659.3 s  ClockTime = 37707 s
as you can see the Uz could not be solved and the solver stopped after 1001 iterations.

I attached a plot of the MaxCo at each iteration on a semi logaritmic scale. As you can see, after the "jump" the Courant decrease and goes back to value around 1.7-2 as I want it. Then after a while a second jump happens.

This is the fvScheme

Code:
ddtSchemes
{
    default         backward;
}

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

divSchemes
{
    default         none;
    div(phi,U)      Gauss linear;
    div(phi,k)      Gauss limitedLinear 1;
    div(phi,B)      Gauss limitedLinear 1;
    div(phi,nuTilda) Gauss limitedLinear 1;
    div(B)          Gauss linear;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
    laplacian(nuEff,U) Gauss linear corrected;
    laplacian((1|A(U)),p) Gauss linear corrected;
    laplacian(DkEff,k) Gauss linear corrected;
    laplacian(DBEff,B) Gauss linear corrected;
    laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
}

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

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p               ;
}
and this the fvSolution

Code:
solvers
{
    p
    {
        solver PCG;
        preconditioner DIC;
        tolerance 1e-06;
        relTol 0.05;
    };

    pFinal
    {
        solver PCG;
        preconditioner DIC;
        tolerance 1e-06;
        relTol 0;
    };

    U
    {
        solver           PBiCG;
        preconditioner   DILU;
        tolerance        1e-08;
        relTol           0;
    };

    UFinal
    {
        solver           PBiCG;
        preconditioner   DILU;
        tolerance        1e-08;
        relTol           0;
    };
    nuTilda
    {
        solver           PBiCG;
        preconditioner   DILU;
        tolerance        1e-07;
        relTol           0;
    };
}

PIMPLE
{
    nCorrectors     2;
    nNonOrthogonalCorrectors 1;
    nOuterCorrectors 2;
}


relaxationFactors
{
    "U.*"               1;
    "nuTilda.*"         1;
}

What should i do? Thank you very much
Attached Images
File Type: png maxCo.png (16.4 KB, 5 views)
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Old   May 6, 2014, 12:23
Default
  #2
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Olivier
Join Date: Jun 2009
Location: France, grenoble
Posts: 238
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hello,
add limiter to div(phi,U), like the limitedLiner you use after, or an other.

regards,
olivier
olivierG is offline   Reply With Quote

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