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Old   August 16, 2007, 10:38
Default LES and immersed boundaries
  #1
kat
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Hi

I'm trying to implement the LES model in a code that uses immersed boundaries in a cartesian grid. How would you treat the walls?

It is difficult to use dynamic procedures since there is now obvious way to do averaging.

Using "simply" Van Driest: how do I determine the distance to a wall?

What other method could I use?

Thanks for your help!

Katrien
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Old   August 16, 2007, 11:17
Default Re: LES and immersed boundaries
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agg
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LES does not provide solutions for near wall region. There are only 2 ways to treat near wall region.

1) High resolution near wall boundary, which could prove costly 2) Use the analytical wall function to determine y+ and then u+ at the first grid point away from the wall. You can find this in any standard CFD text.
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Old   August 17, 2007, 02:37
Default Re: LES and immersed boundaries
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kat
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Indeed, I was planning to go for option 2. How do you determine the distance from the wall with immersed boundaries? Any reference?
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Old   August 23, 2007, 03:13
Default Re: LES and immersed boundaries
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Alexey
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In order to determine the distance from the wall you should use any geometry textbook. Just drop a perpendicular from the point on wall surface and then determinte point of intersection. Knowing coordintes of two points you can easy calculate this distance. What about 3D space imagination?

I would like to advise you to apply improved Smagorinsky model which does not requare knowing of this distance. Look

By E. Leveque, F.Toschi, L.Shao and J.-P. Bertoglio, Shear-improved Smagorinsky model for large-eddy simulation of wall-bounded turbulent flows.// J.Fluid Mech (2007) vol 570, pp 491-502.

This model is much more simpler then classical dynamic model. I used it for LES channel calculations and got very good results. Even for Re_tau = 1000...5000.

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Old   September 17, 2007, 15:47
Default Re: LES and immersed boundaries
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emmanuel Lévêque
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dear alexey,

nice to see that the SISM is already used in practical applications. interested in details of your LES using SISM

best, Emmanuel Lvque

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