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The convective scheme for Implicit LES

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Old   May 13, 2020, 09:14
Default The convective scheme for Implicit LES
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lipeng
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Hello, everyone
Recently, I started to use LDK and smagorinsky to simulate the flow over the cylinder at Re = 20 000. After a trial and error of mesh, I found that Cp and Cp' curves have a excellent agreement with experiment data by "ILES" ,(which means that Ck for Smagorinsky model is 0) when the the scheme of convective term is LUST and the gradp is fourth.

However, I just knew that most cases of ILES is running with the scheme of convective term of TVD.

So, I have two questions:
1, I noticed that there is an option called "Limited linear divergence scheme" in TVD scheme, which can be set at a fixed value of blender to get an equivalent result of LUST. Does it means that LUST can be deemed a variant of TVD ?

2, If LUST is unable to be viewed as one of the TVD. Can I call my case as imlpilcit LES ?
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Old   May 15, 2020, 11:55
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I'll take a stab at providing some context for ILES. In my experience ILES refers to what sort of SGS modeling is present (or lack thereof) -- it is not impacted by choice of divergence schemes -- the LES is just implicit because dissipation is strictly numerical. This is not to say that the divergence schemes have no impact on your solution -- and getting to your first question limitedLinear is the foam flavor of the Sweby limiter (https://en.wikipedia.org/wiki/Flux_limiter) if I recall correctly. You essentially set the around of limiting with the coefficient used. By contrast LUST is a fixed blend of linear and linearUpwind (75 to 25 percent). You might get similar results using the two, but that doesn't mean the schemes are the same.

Caelan
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Old   May 18, 2020, 12:17
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Thank you so much for your excellent anwser !
I read some references about ILES which explain sth clear and bring me more perplexing quations.It seems that only two things are important for ILES, a non-oscillating convect scheme and a set of proper grid.
Moreover, ILES always have a not bad performance for incompressible flow, especially for the velocity profile of channel flow. It is the most close result compared with DNS in some articles. As a result, ILES appears a pretty economical choice.
So, what on earth role do the explicit SGS models play in LES ? How much are they impacted by the numerical scheme ?

Liet
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Old   May 18, 2020, 13:09
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If you're wondering why LES exists, there is a wealth of literature available... but in brief you are applying a low pass filter (hopefully, see e.g. https://en.wikipedia.org/wiki/Filter...dy_simulation)) somewhere in the inertial/self-similar region of the energy cascade -- higher frequency content is then modeled (the model has been constructed to reproduce the behavior of some flavor of turbulence). With ILES there is no modeling and dissipation is numerical and the result of insufficient resolution (if the grid is too coarse; if fine enough the error can be small to negligible).

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