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-   -   Biharmonic Viscosity with Smagorinsky model (http://www.cfd-online.com/Forums/main/4727-biharmonic-viscosity-smagorinsky-model.html)

 Wen Long May 14, 2002 12:54

Biharmonic Viscosity with Smagorinsky model

Dear friends:

I'm working on a nearshore Boussinesq wave model. Currently I have a problem with numerical stability for some cases. In order to damp out small scale noises, I want to use biharmonic damping term with an artificial viscosity given in light of Smagorinsky (1963) and (1993).

While I'm trying to implement it on a curvilinear coordinate, can anyone point me to a reference of biharmonic term calculation in general coordinates? Since it appears to me that the biharmonic operator \nabla^4 in non-orthogornal coordinates is quite complicated.

Thanks,

Wen

 Kalyan May 14, 2002 15:48

Re: Biharmonic Viscosity with Smagorinsky model

If you introduce a biharmonic operator, you are changing the order of the PDEs. You would need additional boundary conditions.

If the biharmonic term is merely an artifact that the numerical equations need, please make sure that the term zeros out near the boundaries. The Smagorinsky viscosity (I guess you are refering to the LES model) does not (and does need to) go to zero at the boundaries.

You may find the discrete biharmonic operator on general coordinates in papers involving transonic flow solvers.

 wen long May 14, 2002 23:39

Re: Biharmonic Viscosity with Smagorinsky model

Dear Kalyan:

Thank you very much. I wasn't aware that I'll have to zero out the viscosity near boundaries. That could be hard if my domain has arbitrarily shaped islands in side.

Yes my biharmonic damping will be only artificial part. Many people do Smagorinsky closure in LES and Large Scale Ocean Turbulence, but papers I got are too concise to gain much out of them.

You mentioned transonic flow solvers, can you point it to me more clearly? I'll try to find sth in my lib.

Thanks again,

Wen

 versi May 15, 2002 05:50

Re: Biharmonic Viscosity with Smagorinsky model

-coef *( Q_{i-2}-4 Q_{i-1} +6 Q_i +4 Q_{i+1} +Q_{i+2}) for equal sized grid. But coef is quite empirical.

 versi May 15, 2002 05:54

Re: Biharmonic Viscosity with Smagorinsky model

Sorry , there should be "-" before "4".

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