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to how much turbulent kinetic energy is resolved from Openfoam LES results ? 

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January 26, 2013, 20:24 
to how much turbulent kinetic energy is resolved from Openfoam LES results ?

#1 
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Dear All,
After finishing a LES case using OPenfoam, I have the thinking to check how much turbulent kinetic energy (for instance 70% or 80%) is resolved based on this case's mesh and results. This can give me some feedback about the mesh or some numerical schemes. Does anybody know how to do this for the Openfoam LES results? best regards, H 

January 27, 2013, 19:41 

#2 
Senior Member

Hi H,
In my opinion, you can do this in two ways: 1) From the LES analysis you will have access to the mean and rms of the resolved velocity  you will want to check that the rms of velocity are converged. You can then calculate the resolved tke based on the rms of velocity. The unresolved can be calculated from the contribution of the SGS turbulence model. 2) Alternatively you could also look at the spectral distribution of the resolved turbulent structure using spatial FFT. This may have issues when coherent structures.
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 Julien de Charentenay 

February 5, 2013, 08:04 

#3  
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Quote:
Thank you so much for your help. For the method 1 you mentioned, I need to obtain the mean and rms quantities on a runtime basis. I think I can these quantities from UPrime2Mean. But I found that even if I defined the fieldAverage1 in controlDict, I can not use these quantities in, e.g. createFields.H files. So how can I access to the these mean and variance during the simulation? Thank you. 

February 6, 2013, 19:10 

#4 
Senior Member

Hi H,
You may not need to do it during the simulation (i.e runtime), but just as a postprocessing. From a practical perspective, I am not able to help... I have done it in the past but with a different solver (starcd) at postprocessing stage only. I can't help with openFoam side... Julien
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 Julien de Charentenay 

April 1, 2016, 06:11 

#5 
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Wen Xu
Join Date: May 2014
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Dear Julien,
Could you give some more details or some references how to calculate the resolved kinetic energy and unresolved kinetic energy? The resolved kinetic energy is equal to k? K=0.5*sqrt(UUmean)? which variable can be characterize the unresolved kinetic energy? Could you give the formulation of them? Thank you in advance! Best, Xu 

April 1, 2016, 06:18 

#6 
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April 1, 2016, 08:59 

#7  
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Wen Xu
Join Date: May 2014
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Quote:
I have read the paper by Pope, thank you very much. But could you give some more details how to calculate the unresolved part? e.g. Could you give the formulation of it? What do you mean " calculated from the contribution of the SGS turbulence model."?? Thank you again! Best, Xu 

April 1, 2016, 09:10 

#8 
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probably you can think about how the k is calculated for the LES model?


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