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Courant Number increasing too high PimpleFoam

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Old   January 11, 2021, 08:14
Default Courant Number increasing too high PimpleFoam
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Hi all,

This is a question which has been asked many times, unfortunately trying some of the suggestions applicable to my situation have not worked, so I hope someone can help now

I have a simulation over open terrain. Over the weekend I simulated the flow using PimpleFoam over a coarse domain using a deltaT of 0.001 and a maxCo of 0.9. It ran for over 3 minutes, (the time I required it to run for), without the courant number increasing above 0.005.

However, when I increase the blockMesh resolution even slightly to (15 10 4) from (10 5 2) shown in my blockMesh file below, with the same deltaT of 0.001, the courant number increases past 1 within 15 minutes and grows exponentially until it crashes. This is an issue, as it isn't close to how fine I need my resolution to be for the study

My checkMesh produces no errors, with a max Non orthogonality of 56, average of 5.

Finally, even with a maxCo of 0.9, using adjustTimeStep causes it to rise above 1 more quickly than without

my case files are shown below

blockMeshDict

convertToMeters 1;

vertices
(
(-125 518150 0)
(2180 518150 0)
(2180 519320 0)
(-125 519320 0)
(-125 518150 450)
(2180 518150 450)
(2180 519320 450)
(-125 519320 450)

);

blocks
(
hex (0 1 2 3 4 5 6 7) (10 5 2) simpleGrading (1 1 1)
);

edges
(
);

boundary
(
outlet
{
type patch;
faces
(
(0 4 7 3)
(1 5 4 0)
);
}

inlet
{
type patch;
faces
(
(2 6 5 1)
( 3 7 6 2 )
);
}
DuneField
{
type wall;
faces
(
(0 3 2 1)
);
}
top
{
type patch;
faces
(
(4 5 6 7)
);
}
);

mergePatchPairs
(
);


fvSchemes:

ddtSchemes
{
default Euler;
}

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

divSchemes
{
default none;
div(phi,U) bounded Gauss linearUpwind grad(U);
div(phi,k) bounded Gauss upwind;
div(phi,epsilon) bounded Gauss upwind;
div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear orthogonal ;
}
interpolationSchemes
{
default linear;
interpolate(U) linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p ;
}

wallDist
{
method meshWave;
}

fvSolution

solvers
{
p
{
solver GAMG;
tolerance 1e-5;
relTol 0.01;

smoother DICGaussSeidel;

cacheAgglomeration true;
nCellsInCoarsestLevel 10;
agglomerator faceAreaPair;
mergeLevels 1;
}

pFinal
{
$p;
relTol 0;
}

"(U|k|epsilon)"
{
solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-05;
relTol 0.1;
}

"(U|k|epsilon)Final"
{
$U;
relTol 0;
}
}

PIMPLE
{
nNonOrthogonalCorrectors 0;
nCorrectors 2;
}

controlDict:

application pimpleFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 10000000000;

deltaT 0.002;

writeControl adjustableRunTime;

writeInterval 1;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;

adjustTimeStep yes;

libs ("libatmosphericModels.so");

maxCo 0.9;


transportProperties

transportModel Newtonian;

nu nu [ 0 2 -1 0 0 0 0 ] 1e-05;

CrossPowerLawCoeffs
{
nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1e-06;
nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;
m m [ 0 0 1 0 0 0 0 ] 1;
n n [ 0 0 0 0 0 0 0 ] 1;
}

BirdCarreauCoeffs
{
nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1e-06;
nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;
k k [ 0 0 1 0 0 0 0 ] 0;
n n [ 0 0 0 0 0 0 0 ] 1;
}

turbulenceProperties


simulationType RAS;

RAS
{
RASModel RNGkEpsilon;

turbulence on;

printCoeffs on;

kEpsilonCoeffs
{
Cmu 0.09;
C1 1.44;
C2 1.92;
sigmaEps 1.11;
}
}



If any other files are needed, please let me know. Any advice would be greatly appreciated

Last edited by CfdUser5855; January 11, 2021 at 08:16. Reason: Missing File
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