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Total Reynolds Stress and Turbulence Energy Spectrum of LES

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Old   July 10, 2013, 18:16
Default Total Reynolds Stress and Turbulence Energy Spectrum of LES
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realM
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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 (Relation between k and UPrime2Mean etc in LES),
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
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Old   November 13, 2013, 04:55
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Giulio S
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Quote:
Originally Posted by sanysaly View Post
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 (Relation between k and UPrime2Mean etc in LES),
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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Old   January 24, 2015, 16:28
Default Total Reynolds Stress in LES
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Hi GiulioS,

This is an old post but i see you have suggested to calculate total Reynolds stress by considering
total Reynolds Stress = UPrime2Mean + Subgrid_ReynoldsStress.

But, my question is in the LES tutorial channel395, openFoam calculates reynolds stress only using UPrime2Mean, so which is correct?


postChannel utility.
Code:
     volScalarField Rxy(UPrime2Mean.component(symmTensor::XY));


     makeGraph(y, RxyValues, "uv", path, gFormat);

So which method is correct? I saw Eugene De Villiers also suggested your method. But I am confused now.

Thank you.
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