Turbulent models at high Reynolds number

mayj · October 7, 2013, 01:17

Hi
What are the major differences between LES, K-Epsilon and DES models in high Reynolds number in OBCs, in 2D and 3D method?
your reply will be highly appreciated.
Thanks

ghorrocks · October 7, 2013, 06:00

Please do not use jargon as people have no idea what you are talking about - fortunately Lance has nicely pointed that out in this thread: http://www.cfd-online.com/Forums/cfx...ds-number.html

So a general comment abotu turbulence models:
* k-eps is a general purpose 2-eqn turbulence model. It works by modelling all turbulence as extra viscosity. I prefer the SST 2-eqn turbulence mode myself for general stuff, but the k-eps model is OK for many applications. Most engineering work uses either SST ot k-eps.
* LES is a sophistocated modelling approach where you split the turbulent spectrum into resolved and non-resolved components. This means you have to resolve the larger turbulence scales which means fine mesh, small time steps and low dissipation numerics. LES is not for beginners, so if you are asking what is LES then it is not suitrbale for you.
* DES is a combination of 2-eqn models and LES where the model attempts to use LES approaches in regions suitable for it, and a simpler 2-eqn model where that is appropriate. This is even more complex than LES so again not suitbale for beginners.

October 7, 2013, 01:17	Turbulent models at high Reynolds number	#1
mayj Member may Join Date: Jul 2013 Posts: 31 Rep Power: 12	Hi What are the major differences between LES, K-Epsilon and DES models in high Reynolds number in OBCs, in 2D and 3D method? your reply will be highly appreciated. Thanks

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October 7, 2013, 06:00		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,697 Rep Power: 143	Please do not use jargon as people have no idea what you are talking about - fortunately Lance has nicely pointed that out in this thread: http://www.cfd-online.com/Forums/cfx...ds-number.html So a general comment abotu turbulence models: * k-eps is a general purpose 2-eqn turbulence model. It works by modelling all turbulence as extra viscosity. I prefer the SST 2-eqn turbulence mode myself for general stuff, but the k-eps model is OK for many applications. Most engineering work uses either SST ot k-eps. * LES is a sophistocated modelling approach where you split the turbulent spectrum into resolved and non-resolved components. This means you have to resolve the larger turbulence scales which means fine mesh, small time steps and low dissipation numerics. LES is not for beginners, so if you are asking what is LES then it is not suitrbale for you. * DES is a combination of 2-eqn models and LES where the model attempts to use LES approaches in regions suitable for it, and a simpler 2-eqn model where that is appropriate. This is even more complex than LES so again not suitbale for beginners.