# [LES] Reynolds stresses are lower than DNS

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March 29, 2020, 13:10
[LES] Reynolds stress(w'w') is lower than DNS
#1
Senior Member

Join Date: Jan 2018
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Hi,

I simulated a duct flow using Dynamic Smagorinsky model.
The simulation is completely converged.
The <w'w'> component of Reynlods stress is about half of DNS (you can see it in the attached image) while the mean streamwise velocity profile has a good agreement with DNS.

Anyone knows why?

Thank you.
Attached Images
 LES.png (18.0 KB, 14 views)

Last edited by Moreza7; March 29, 2020 at 17:15.

March 29, 2020, 14:29
#2
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Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,198
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Quote:
 Originally Posted by Moreza7 Hi, I simulated a duct flow using Dynamic Smagorinsky model. The simulation is completely converged. The and components of Reynlods stress are about half of DNS (you can see it in the attached image) while the mean streamwise velocity profile has a good agreement with DNS. Anyone knows why? Thank you.

How did you compute the RMS?

March 29, 2020, 17:07
#3
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Quote:
 Originally Posted by FMDenaro How did you compute the RMS?
I used Code Saturne for simulation, calculated <w>^2 and <w^2> and used the following equation:

( is mean wall shear stress over 4 walls)
The other Reynolds stress components are pretty good.

 March 29, 2020, 17:33 #4 Senior Member   Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,198 Rep Power: 66 I suggest to check further your RMS. The comparisons we did showed Code_Saturne overestimates the DNS peaks for the plane channel flow, see https://www.researchgate.net/publica...mulation_codes maybe the statistically averaged velocity is not well computed Moreza7 likes this.

 March 30, 2020, 00:51 #5 Member   EM Join Date: Sep 2019 Posts: 49 Rep Power: 5 Give some bleeding info about your simulation and that u are comparing with. Document yr flow before you ask a question. what Re? what resolution? whose dns? what is the exact geometry, channel or rec/sq duct? which is the wall-normal and wall parallel component? if duct, where in the cross section are the profiles from? are u including an estimate of the sgs intensity in the stats? show a comparison with all three intensities. -- FMDenaro likes this.

 Tags large eddy simulation

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