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-   -   Nonlinear k epsilon Shih Model (http://www.cfd-online.com/Forums/openfoam/73054-nonlinear-k-epsilon-shih-model.html)

idrama February 25, 2010 11:16

Nonlinear k epsilon Shih Model
 
Hallo Foamers!

Does anybody know a reference where I can find the derivation of the Nonlinear k e Shih model?

Cheers

idrama May 21, 2010 03:39

Does really nobody knows a reference, at least one? HELP

idrama May 21, 2010 04:05

Does really nobody knows a reference, at least one? HELP

Moelfus August 24, 2010 04:28

Hi Claus,

the paper you are searching for can be found at the NASA pages. There you have access to a lot of other papers of Shih:

http://ntrs.nasa.gov/search.jsp?R=35...%257c1%26N%3D0

Best regards,

Olli

Thomas Baumann August 25, 2010 10:29

Hi,

have you simulated successful using this turbulence-model?
I have problems near walls (U isn't zero orthogonal to the wall in the nearwall-part even in channel-flows).

Regards Thomas

Moelfus August 26, 2010 05:29

Hi,

yes I'm using this turbulence model for simulating swirling flows. For this purpose it seems to be perfect. I haven't discovered any problems until know.

Olli

Thomas Baumann August 26, 2010 06:11

Hi,
I have velocities out of the wall.
I have described this in a posting here in the forum.

http://www.cfd-online.com/Forums/ope...inearshih.html

But if I'm using a very fine mesh (y+ < 0.4) the results are better. So the solution has a mesh-dependence.
Maybe it's caused by the fvschemss are the solvers for p,U,k...
I have tried different ones without success.

Could you maybe show your fvschemes and the fvSolution-data, please?

Thanks and regards,

Thomas

Moelfus August 27, 2010 07:32

Hi Thomas,

a y+ of less than 0.4 seems to be a sufficient fine mesh. Nevertheless, are k-epsilon models known for their bad boundary layer behaviour. Therefore this model uses an boundary layer model in the near wall region. I can look up how it is set up. If the results have a mesh-dependence you should probably do a grid study :-( An other way would be to use an much coarser mesh, if boundary layers are not prior-ranking.

Olli

fvSchemes:
-----------------------------------------------------------------

ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
grad(U) Gauss linear;
// grad(U) cellLimited Gauss linear 1;
}

divSchemes
{
default none;
div(phi,U) Gauss linearUpwindV Gauss linear;
div(phi,k) Gauss upwind;
div(phi,omega) Gauss upwind;
div((nuEff*dev(grad(U).T()))) Gauss linear;
div(nonlinearStress) Gauss linear;
div(phi,epsilon) Gauss upwind;
div(phi,R) Gauss upwind;
div(R) Gauss linear;
div(phi,nuTilda) Gauss upwind;
}

laplacianSchemes
{
default Gauss linear corrected;
// default Gauss linear limited 0.5;
// default Gauss linear limited 0.333;
laplacian(nuEff,U) Gauss linear corrected;
laplacian((1|A(U)),p) Gauss linear corrected;
laplacian(DkEff,k) Gauss linear corrected;
laplacian(DepsilonEff,epsilon) Gauss linear corrected;
laplacian(DREff,R) Gauss linear corrected;
laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;

}

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

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p;
}

fvSolution:
-------------------------------------------------------

solvers
{
p
{
solver GAMG;
preconditioner FDIC;
mergeLevels 1;
smoother GaussSeidel;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 100;
tolerance 1e-06;
relTol 0.01;
}

U
{
solver GAMG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
mergeLevels 1;
smoother GaussSeidel;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 100;
tolerance 1e-05;
relTol 0;
}

k
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}

epsilon
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}

R
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}

nuTilda
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
}

relaxationFactors
{
p 0.2;
U 0.5;
k 0.7;
epsilon 0.7;
R 0.7;
nuTilda 0.7;
}

Thomas Baumann August 27, 2010 12:05

Hi,

thank you very much.

I have simulated using your given condition, but the velocities didn't get better.
Have you ever simulated a non-swirling flow using this model?

Regards Thomas

Moelfus August 30, 2010 10:37

Hi,

no, I never simulated a non-swirling case with this model. I just used the model because all other models either crashed or over predicted the axial velocity. I looked at your other post and really have no idea what is going wrong there.

Olli


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