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- - **Limiting turbulent viscosity**
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Limiting turbulent viscosityHi,
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 |

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