RANS vs LES

April 26, 2005, 10:40

Hi,

Can anyone here explain the differences between RANS and LES? When to choose one and not the other? Or please advise me websites that discusses these. Thanks!

Pei

April 26, 2005, 18:48

RANS corresponds to an average of several repetitions of the same turbulent process so that mean values are obtained.

LES simulates the turbulent structures (not all but the ones with a scale larger than the resolution asked by the user).

As mean values are smoother to solve than the eddies roll-over, RANS demands less computational efforts than LES.

For the turbulent scales which are to small to be solved in LES, turbulent models are localy applied to evaluate the overall level of turbulence with structure scales smaller than the resolved scale. These SubGgrid Scale models (because the resolved scale is given more or less by the grid size) may have some common points with RANS models even if the underlying theories are conceptually different.

April 27, 2005, 09:40

Thanks Guillaume!

Pei

April 26, 2005, 10:40	RANS vs LES	#1
Pei Hsieh Guest Posts: n/a	Hi, Can anyone here explain the differences between RANS and LES? When to choose one and not the other? Or please advise me websites that discusses these. Thanks! Pei

April 26, 2005, 18:48	Re: RANS vs LES	#2
Guillaume Guest Posts: n/a	RANS corresponds to an average of several repetitions of the same turbulent process so that mean values are obtained. LES simulates the turbulent structures (not all but the ones with a scale larger than the resolution asked by the user). As mean values are smoother to solve than the eddies roll-over, RANS demands less computational efforts than LES. For the turbulent scales which are to small to be solved in LES, turbulent models are localy applied to evaluate the overall level of turbulence with structure scales smaller than the resolved scale. These SubGgrid Scale models (because the resolved scale is given more or less by the grid size) may have some common points with RANS models even if the underlying theories are conceptually different.

April 27, 2005, 09:40	Re: RANS vs LES	#3
Pei Hsieh Guest Posts: n/a	Thanks Guillaume! Pei

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