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-   -   Total Reynolds Stress and Turbulence Energy Spectrum of LES (http://www.cfd-online.com/Forums/openfoam-verification-validation/120612-total-reynolds-stress-turbulence-energy-spectrum-les.html)

sanysaly July 10, 2013 19:16

Total Reynolds Stress and Turbulence Energy Spectrum of LES
 
Hi,
I am doing LES with pisoFoam. My questions that may be useful as post-processing tools and/or as a utility for validation of model are:
1- How can we calculate the Total Reynolds Stress? Based on thread (http://www.cfd-online.com/Forums/ope...tml#post342243),
We just need to “UPrime2Mean + RMean” (respectively resolved + SGS parts) to get the full stresses. But, is this calculation valid for LES (pisoFoam)?
2- Is there any way to calculate “turbulence energy spectrum” of LES directly in openFoam ?
Thanks

GiulioS November 13, 2013 04:55

Quote:

Originally Posted by sanysaly (Post 439053)
Hi,
I am doing LES with pisoFoam. My questions that may be useful as post-processing tools and/or as a utility for validation of model are:
1- How can we calculate the Total Reynolds Stress? Based on thread (http://www.cfd-online.com/Forums/ope...tml#post342243),
We just need to “UPrime2Mean + RMean” (respectively resolved + SGS parts) to get the full stresses. But, is this calculation valid for LES (pisoFoam)?
2- Is there any way to calculate “turbulence energy spectrum” of LES directly in openFoam ?
Thanks

Dear sanysaly
The pisoFoam solver gives you the UPrime2Mean,referred to the "filtered scale", just like sad in the thread mentioned, so you have to add the contribution from the "SGS scale", just like:
(2.0/3.0)*I)*k_ - nuSGS_*twoSymm(fvc::grad(U_) ,
if you want to have the full Reynolds stress tensor.
For the second question, I suggest to calculate in an external software, just like twice the Fourier transform of the autocovariance.
Giulio S


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