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-   -   Limiting turbulent viscosity (http://www.cfd-online.com/Forums/openfoam/92608-limiting-turbulent-viscosity.html)

cm_jubayer September 19, 2011 17:24

Limiting turbulent viscosity
 
Hi,

I want to limit turbulent viscosity but I don't know how to do that in OpenFOAM. Can someone please help me with this :confused:? Thanks.

Jubayer

cm_jubayer September 21, 2011 14:27

Hi, I am using pisoFoam and my fvSchemes is as follows:

ddtSchemes
{
default Euler;
}

gradSchemes
{
default cellMDLimited Gauss linear 0.5;
grad(p) cellMDLimited Gauss linear 0.5;
grad(U) cellMDLimited Gauss linear 0.5;
// grad(U) cellLimited Gauss linear 1;
}

divSchemes
{
default none;
div(phi,U) Gauss limitedLinearV 1;
div(phi,k) Gauss limitedLinear 1;
div(phi,omega) Gauss limitedLinear 1;
div((nuEff*dev(grad(U).T()))) Gauss linear limited 0.5;
}

laplacianSchemes
{
default none;
laplacian(nuEff,U) Gauss linear limited 0.5;
laplacian((1|A(U)),p) Gauss linear limited 0.5;
laplacian(DkEff,k) Gauss linear limited 0.5;
laplacian(DomegaEff,omega) Gauss linear limited 0.5;

}

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

snGradSchemes
{
default limited 0.5;
}

fluxRequired
{
default no;
p;

}

What should I do if I want to limit my nu to specific values like 0 to 1e6?


Jubayer

vkrastev September 22, 2011 06:20

In order to limit the turbulent viscosity you have to modify the source file related to the turbulence model you are using, by adding a limiter in the eddy (turbulent) viscosity calculation formula. Anyway, I don't know what is your application, but you should be careful in adding an arbitrary limiter in a pre-existing turbulence model.

V.

cm_jubayer September 22, 2011 09:54

Thanks Vesselin for your reply.

Jubayer

cm_jubayer September 29, 2011 09:54

Hi,

To bound nut, I have added this line to the LaunderSharmaKE model,

bound(nut_, dimensionedScalar("0", nut_.dimensions(), 10.0));

After compiling and everything, at each time step it showed me the bounding values. But this is not actually bounding the values as I can see that the nut values are going above 10. Can someone please explain me how this bounding actually works? Thanks.

Jubayer

cheng1988sjtu April 6, 2015 14:18

This depends on how to calculate the eddy viscosity, usually the unexpected large eddy viscosity is caused by the deviding a relative small value, for example, in k-Epsilon model, nut = C*k^2/epsilon, to limit the eddy viscosity, an effective way is to limit the smallest epsilon value (but not unphysically large).

Charlie


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