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-   -   have anybody use the LES in CFX? (http://www.cfd-online.com/Forums/cfx/25540-have-anybody-use-les-cfx.html)

Wei March 26, 2008 10:42

have anybody use the LES in CFX?
 
Hi, everybody.

Did someone have use the LES in CFX? if someone have do a CFD on a ribbed channel or a U-bend channel using the LES in CFX, Could you tell me the result? is it better than any RANS?

Thank you!

Wei.

Glenn Horrocks March 26, 2008 17:26

Re: have anybody use the LES in CFX?
 
Hi,

Whether LES is better than RANS depends on what you are trying to do! The literature shows many examples when RANS gives a more accurate result than LES.

CFX can do LES. There has been many posts on the issue on this forum recently. Also look in the CFX documentation as it discusses the LES models it has.

Glenn Horrocks

Wei March 26, 2008 21:54

Re: have anybody use the LES in CFX?
 
thank you, Horrocks. you said, there are many examples show the RANS gives a more accurate result than LES. But, according to the literature I have read. the LES is better than RANS almost. As you said, It may be depend on the issue. My research problem have big separation, reattachment,and second flow. In a word, the flow is too complicated.

Kushagra April 17, 2008 19:34

Re: have anybody use the LES in CFX?
 
try out one LES simulation...setting up LES in CFX is very simple..just you need a fine mesh and a small time step.... take a time step based on your guess on RANS experience, see the residuals....and then decide if you need to decrease.....each time step should converge within 3-4 or 5 iterations.....otherwise use adaptive time step scheme...

only one problem so far with LES in CFX that I have found that 'opening' type boundary condition may cause the linear solver to fail...same has been mentioned in the CFX documents...

so give it a try.......in my case the flow is highly complicated..still no initial flow field was required....you can give some RANS soution as initial guess...it will converge faster...

Hope it helps and Good luck !

Kushagra



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