Resolved Reynolds Stress in LES

yinyueqiang · July 23, 2013, 21:40

Hi All,

I am running a case using LES on Fluent, and trying to get the Reynolds stress(<u1'u2'>) distribution on some locations of the computation domain. So after my case have been running and averaged for abundant time, I click Results->Plot->Unsteady Statistics, and then found "Resolved UV Reynolds Stress". Does anyone know how this "Resolved UV Reynolds Stress" is defined? Is it still <u1'u2'> ? By indicating "Resolved", does it mean there is another part of (unresolved) Reynolds stress not included here? Thank you very much.

-Steve

flotus1 · July 24, 2013, 03:21

That is the basic idea behind LES. Only the large scales are resolved while the small scales are still modeled ("eddy viscosity").
Thus "Resolved Reynolds Stress" is the best guess for the actual Reynolds Stresses. In a well-resolved LES, the resolved part should be >90% of the total Reynolds stresses.

yinyueqiang · July 24, 2013, 11:16

Quote:

Originally Posted by flotus1

That is the basic idea behind LES. Only the large scales are resolved while the small scales are still modeled ("eddy viscosity").
Thus "Resolved Reynolds Stress" is the best guess for the actual Reynolds Stresses. In a well-resolved LES, the resolved part should be >90% of the total Reynolds stresses.

Many thanks Alex.

You mentioned the "Resolved Reynolds Stress" is only one part of the Reynolds stresses(the resolved part). Do you know if there is any method with which I can get the whole Reynolds stresses(not only the resolved part, but also the modeled part)? thanks again.

Steve

flotus1 · July 24, 2013, 11:48

Apart from a DNS, I cant think of a reliable method to obtain the "exact" Reynolds stresses.
But as already mentioned, if the LES is well-resolved, the differences should be negligible.

July 23, 2013, 21:40	Resolved Reynolds Stress in LES	#1
yinyueqiang New Member Steve Join Date: Feb 2013 Posts: 3 Rep Power: 13	Hi All, I am running a case using LES on Fluent, and trying to get the Reynolds stress(<u1'u2'>) distribution on some locations of the computation domain. So after my case have been running and averaged for abundant time, I click Results->Plot->Unsteady Statistics, and then found "Resolved UV Reynolds Stress". Does anyone know how this "Resolved UV Reynolds Stress" is defined? Is it still <u1'u2'> ? By indicating "Resolved", does it mean there is another part of (unresolved) Reynolds stress not included here? Thank you very much. -Steve Last edited by yinyueqiang; July 23, 2013 at 21:41. Reason: missed some info

July 24, 2013, 03:21		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	That is the basic idea behind LES. Only the large scales are resolved while the small scales are still modeled ("eddy viscosity"). Thus "Resolved Reynolds Stress" is the best guess for the actual Reynolds Stresses. In a well-resolved LES, the resolved part should be >90% of the total Reynolds stresses. yinyueqiang and jzc like this.

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July 24, 2013, 11:48		#4
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Apart from a DNS, I cant think of a reliable method to obtain the "exact" Reynolds stresses. But as already mentioned, if the LES is well-resolved, the differences should be negligible.