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-   -   __LES Questions__ (http://www.cfd-online.com/Forums/openfoam/84348-__les-questions__.html)

maysmech January 26, 2011 17:19

__LES Questions__
 
Dear Foamers,
Two questions about LES model:

1- What is U or P in this model. is it filtered one or real one. i mean U and P which are results and be written in folders and their initials which is at 0 folder.

2- It is not a filteration process in oneEqEddy or smagorinsky models but there is available for DynSmagorinsky. Why?

http://foam.sourceforge.net/doc/Doxy...agorinsky.html

http://foam.sourceforge.net/doc/Doxy...agorinsky.html

Thanks in advance,

cheng1988sjtu January 26, 2011 23:04

my understanding
 
1. I think the U and P in the result are real one rather than filtered, filtering process is internal process, and basically we are combing resolved and sub-filtering scale to present the real result.

2. since the smagorinsky and oneEqnEddy model are two-level filtering model, dynSmagorinsky model are three filtering model. To avoid the a possible loss of efficiency of classical Germano-Lilly dynamic procedure, the scale-dependent dynamic procedure is obtained by considering a second test filtering level. please see "Large Eddy Simulation For Incompressible Flow" Third Edition, Page142, by Pierre Sagaut.

Above is my shallow understanding of your question, if anything wrong, please let me know, thanks!

Farshad_Noravesh January 27, 2011 02:56

prove it please!
 
Hi Foamers,

Thanks for this nice discussions. I appreciate you.
please show me where the real U and P are constructed by the filtered one.
My poor understanding is because only the LES pointer is selected by runtime mechanism ,only and only the subgrid scale model is written in terms of filtered variables and therefore the overall equation only contains filtered variables. Please correct me if i am wrong. And also the boundary variables should be set after manual filteration!
Thanks alot
Farshad

cheng1988sjtu January 27, 2011 10:34

SGS stress
 
Hi,

Nice discussion really!

As far as I know, in LES model, the effect of the resolved subfilter-scale (RSFS) and subgrid-scale (SGS) motions on the resolved velocity field must be modeled.

The RSFS contribution can be theoretically reconstructed, and the SGS stress must be modeled, in DynSmagorinsky we use Germano-Lilly eddy-viscosity SGS model in which the total parameter C*delta is calculated dynamically.

So the solution has filtered and subfiltered components in itself.

Again, it's just my understanding on that, please let me know if I'm wrong.:)

maysmech January 27, 2011 10:52

Thanks for your contributions.
Do you know in which place of OpenFOAM filtering of parameters occured? i need its source file.
Regards.

cheng1988sjtu January 27, 2011 11:40

link to the filter
 
Hi,

since there are many different type of filters, take simpleFilter as an example. you can refer to the following link:

http://foam.sourceforge.net/doc/Doxy...8C_source.html
:D


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