Turbulence Model L.E.S

hamoudi · June 21, 2009, 06:13

Good Moning Everybody,

Please if every one can answer me, i am doing a simulation in 2D
Can i use L.E.S as a turbulence Model in 2D simulation
because L.E.S turbulence model is very robust

Thank you in advance

Maddin · June 22, 2009, 07:31

You can but sure that you want this?!

vishyaroon · June 23, 2009, 10:53

If you talk to people who work with LES, they will frown if you call it a model, because LES resolves the turbulent scales.

I'd say 3D is better. 2D suppresses the vortices and/or turbulence fluctuations in the third direction (that you are not considering) thereby resulting in some underpredictions. I'd not say that 2D is not feasible, but I'd stay away from 2D if I'm doing LES. In fact even 2D cases are sometime handled as 3/2D where you have periodicity in the thrid dimension.

matejfor · July 16, 2009, 08:45

LES is not a robust turbulence model K-eps is robust model. LES resolves turbulence scales and models only the very small ones. If you run 2D LES your results will be rubbish, as the turbulence is not averaged and you must preserve the 3D nature of it. For LES you need much finer grid and small time step and you should know what you're doing. If you want results looking like LES but with cheaper calculation you should try SAS turbulence model (but I do not think it is availible in CCM, you have to go ANSYS to get it).

matej

Maddin · July 16, 2009, 08:52

In CCM you only have DES when you run unsteady. Steady you don't have this, AFAIK.

June 21, 2009, 06:13	Turbulence Model L.E.S	#1
hamoudi Member Hamoudi djamel Join Date: Apr 2009 Posts: 50 Rep Power: 17	Good Moning Everybody, Please if every one can answer me, i am doing a simulation in 2D Can i use L.E.S as a turbulence Model in 2D simulation because L.E.S turbulence model is very robust Thank you in advance

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June 22, 2009, 07:31		#2
Maddin Senior Member Join Date: Mar 2009 Posts: 260 Rep Power: 18	You can but sure that you want this?!

June 23, 2009, 10:53		#3
vishyaroon Senior Member Aroon Join Date: Apr 2009 Location: Racine WI Posts: 148 Rep Power: 17	If you talk to people who work with LES, they will frown if you call it a model, because LES resolves the turbulent scales. I'd say 3D is better. 2D suppresses the vortices and/or turbulence fluctuations in the third direction (that you are not considering) thereby resulting in some underpredictions. I'd not say that 2D is not feasible, but I'd stay away from 2D if I'm doing LES. In fact even 2D cases are sometime handled as 3/2D where you have periodicity in the thrid dimension.

July 16, 2009, 08:45		#4
matejfor Senior Member matej forman Join Date: Mar 2009 Location: Brno, Czech Republic Posts: 182 Rep Power: 17	LES is not a robust turbulence model K-eps is robust model. LES resolves turbulence scales and models only the very small ones. If you run 2D LES your results will be rubbish, as the turbulence is not averaged and you must preserve the 3D nature of it. For LES you need much finer grid and small time step and you should know what you're doing. If you want results looking like LES but with cheaper calculation you should try SAS turbulence model (but I do not think it is availible in CCM, you have to go ANSYS to get it). matej

July 16, 2009, 08:52		#5
Maddin Senior Member Join Date: Mar 2009 Posts: 260 Rep Power: 18	In CCM you only have DES when you run unsteady. Steady you don't have this, AFAIK.