Still confused by LES

smillion · November 23, 2010, 01:42

Hi,

I've been reading so many posts and information on the net regarding LES simulation. They all say that it involves resolving the large scales whereas the smaller scales are modelled.

Does that mean the smaller eddies are simulated because isn't that what 'modelling' means. I know what LES stands for but it seems contradictory if the smaller scales are modelled and the large scales are resolved.

Or maybe I have the wrong idea??

Larsen · November 25, 2010, 18:29

The length of the smallest turbulence motion can be found by using kolmogorovs length scale. In DNS simulation, one solves every motion of turbulence. which requires a hugh mesh.

Since the small turbulence motion does not contribute significantly to the flow properties these are modeled up instead of resolving the directly with navier stockes like in DNS. This is what LES do. By using a larger grid size, only the large turbluence motion is resolved with navier stockes and the small ones are modelled up.

This is the short story. Try reading the book " A first course in turbulence" to get a better insight.

smillion · November 27, 2010, 21:14

Ok thanks Larsen

November 23, 2010, 01:42	Still confused by LES	#1
smillion Member Join Date: Dec 2009 Posts: 33 Rep Power: 16	Hi, I've been reading so many posts and information on the net regarding LES simulation. They all say that it involves resolving the large scales whereas the smaller scales are modelled. Does that mean the smaller eddies are simulated because isn't that what 'modelling' means. I know what LES stands for but it seems contradictory if the smaller scales are modelled and the large scales are resolved. Or maybe I have the wrong idea??

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November 25, 2010, 18:29		#2
Larsen New Member Thomas Larsen Join Date: Apr 2010 Posts: 12 Rep Power: 16	The length of the smallest turbulence motion can be found by using kolmogorovs length scale. In DNS simulation, one solves every motion of turbulence. which requires a hugh mesh. Since the small turbulence motion does not contribute significantly to the flow properties these are modeled up instead of resolving the directly with navier stockes like in DNS. This is what LES do. By using a larger grid size, only the large turbluence motion is resolved with navier stockes and the small ones are modelled up. This is the short story. Try reading the book " A first course in turbulence" to get a better insight.

November 27, 2010, 21:14		#3
smillion Member Join Date: Dec 2009 Posts: 33 Rep Power: 16	Ok thanks Larsen