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Relashionship between subgrid-scale kinetic energy and subgrid-scale iscosity

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Old   May 4, 2015, 09:24
Default Relashionship between subgrid-scale kinetic energy and subgrid-scale iscosity
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Pj.
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Hi everybody.

Inside a paper I found this equation:
k_{sgs}=\left( \frac{\nu_{sgs}}{C_K \Delta} \right)^2
This was applied to a LES case using the static Smagorinsky turbulence model.

I tried to understand where this come from, but with no success.
I found THIS wiki page, but honestly it didn't help me too much. I even started to fear that this applies to a completely different turbulence model, rather than to Smagorinsky one.

___________________________________
Here below I report some though of mine.

I think that it's correct to write that the k_{sgs} is
k_{sgs}=k-k_R
where k_R is the resolved kinetic energy. Now
k=\frac{1}{2} \overline{{u_i^{'}}^2}
where - is the time averaging operator, and
k_{sgs}=\frac{1}{2} \overline{\widetilde{{u_i^{'}}}^2}
where \widetilde{} is the LES space-filtering operator.

In this case the wiki equation seams wrong to me, since in LES should be
\overline{\widetilde{{u_i^{'}}}^2} \neq \overline{{u_i^{'}}}^2
as time-averaging and space-filtering are different operations.

One more thing that I cannot explain myself is that in the Boussinesque hypothesis that relates \tau_{ij} to \nu_T the rate-of-strain tensor appears and I cannot figure how to remove it or relate it to the k_{sgs}.

Any hint would be welcome. Thank you very much.

___________________________________
EDIT:
I found this equation inside a chapter on the Fluent guide http://www.arc.vt.edu/ansys_help/flu...gs_models.html (last sub-chapter in the link). This refers to a paper by Kim & Menon (http://arc.aiaa.org/doi/pdf/10.2514/6.1997-210). This however seams to point in the direction that this equation applies to a different turbulence model, rather than to the Smagorinsky one.

Last edited by Pj.; May 5, 2015 at 12:22.
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