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

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

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.

Thanks Vesselin for your reply.

Jubayer

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

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