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-   -   LES calculation of EPSILON (turbulence dissipation) (http://www.cfd-online.com/Forums/openfoam-post-processing/125999-les-calculation-epsilon-turbulence-dissipation.html)

Gosi November 5, 2013 22:38

LES calculation of EPSILON (turbulence dissipation)
 
hi everybody,

I am using pisoFOAM with LES Smagorinsky model to simulate a fully developed turbulent flow in a rotating pipe.

Now i want to evaluate the turbulence dissipation epsilon.

Is is it possible to calculate or postprocess it with openfoam? Is there anyone who did some kind of postprocessing before?
Any help would be appreciated.

Simon

MaryBau February 21, 2014 13:30

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Hi Simon and everyone;

Did you find the solution to your problem?

I am also trying to calculate de dissipation of an LES simulation, but I am not getting the correct value.

I am doing a decaying isotropic turbulence, then the derivative of the energy with respect to time should be equal to my -dissipation: dE/dt=-epsilon.

If I calculate dE/dt in my simulations, my results are in agreement with a DNS simulation (A. Wray in the AGARD database). However if I calculate epsilon directly from my velocity field, it seems that I have a constant "shift" as you can see in my plot.

I am calculating my disipation as:

volSymmTensorField S(symm(fvc::grad(U)));
volScalarField epsilon=2*(nu+nuSgs)*(S && S); #epsilon total

Any suggestions or ideas of what I might be doing wrong ? Am I missing something?

Thanks for your help and have a nice day,

Mary

sebastien_F1 October 21, 2014 17:29

Hi MaryBau,

Did you get a chance to get it working? I'm also trying to calculate the resolved dissipation rate and it's off by a factor 2 or 3.

Thanks
Sebastien

Shahr October 23, 2014 09:58

In general LES case, not only for decaying turbulence simulation, the correct procedure for calculating total turbulence dissipation seems to be calculating the dissipation tensor of the resolved scale, component by component, and adding it to the contribution of the sub-grid scale (this is my understanding).

The former requires having access to uPrime. When uPrime at each time step is available, one can get derivatives in corresponding directions, and then time-average the value to get one component of the resolved-scale dissipation.This must be done for each component. The procedure seems possible with the help of some additional functionObjects, and then tedious post-processing.

The latter however seems to be impossible using the output of subgrid-scale models in OpenFOAM. What can be taken out of the SGS model is only the magnitude of dissipation at SGS.

So in order to calculate dissipation correctly we have to think about solving each of the a.m. problems. If anybody has any ideas, I would be glad to discuss.


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