# Large Eddy Simulation - LES

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 April 8, 2013, 05:18 Large Eddy Simulation - LES #1 New Member   Join Date: Feb 2013 Posts: 7 Rep Power: 6 Hello all, I want to used a LES to simulate the transport of smoke in an air flow. I know that LES is always unsteady. I have read in "Turbulence Modeling for CFD" by David C. Wilcox and could not find out why LES only can be used unsteady. Could anyone of you please tell me why it's not possible to use LES steady? Thanks

 April 8, 2013, 07:10 #2 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 20 The LES turbulence model is derived by modeling the small scales of the fluid. Formally, it looks like the RANS model, but it has nothing to do with that. Since no time integration / averaging is involved in LES, it just does not behave like that and thus results in transient solutions. __________________ The skeleton ran out of shampoo in the shower.

April 8, 2013, 07:28
#3
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,562
Rep Power: 40
Quote:
 Originally Posted by RodriguezFatz The LES turbulence model is derived by modeling the small scales of the fluid. Formally, it looks like the RANS model, but it has nothing to do with that. Since no time integration / averaging is involved in LES, it just does not behave like that and thus results in transient solutions.
I agree, it is simple to see the LES equation when you start from the NS equation and apply to each term a local filter. As a result, the time derivative of each conserved variable, e.g., mass, momentum, etc., does not vanish.

 April 8, 2013, 08:05 #4 New Member   Join Date: Feb 2013 Posts: 7 Rep Power: 6 So because filtering is not equal to time averaging, the equation is time dependent and i have to regard the time derivative?

 April 8, 2013, 08:19 #5 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 20 Yes. Better think of LES as a slight relaxation of computational efford (compared to DNS), that is bought by a loss of precision. But it's not too different from DNS. __________________ The skeleton ran out of shampoo in the shower.

 April 8, 2013, 08:23 #6 New Member   Join Date: Feb 2013 Posts: 7 Rep Power: 6 Ok, thank you very much. I think i got it.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post sheth Main CFD Forum 4 March 19, 2012 08:22 mariachi FLUENT 1 January 23, 2010 04:36 mariachi FLUENT 9 January 19, 2010 12:55 PattiMichelle Phoenics 2 April 29, 2005 13:24 Parshant Dhand FLUENT 0 May 19, 2003 22:12

All times are GMT -4. The time now is 04:41.

 Contact Us - CFD Online - Privacy Statement - Top