# LES calculation of EPSILON (turbulence dissipation)

 Register Blogs Members List Search Today's Posts Mark Forums Read

 November 5, 2013, 22:38 LES calculation of EPSILON (turbulence dissipation) #1 New Member   Simon Emhardt Join Date: Feb 2013 Posts: 9 Rep Power: 5 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

February 21, 2014, 13:30
#2
Member

Join Date: Jul 2010
Posts: 39
Rep Power: 8
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:

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
Attached Files
 calculatedEdt.pdf (23.3 KB, 130 views)

 October 21, 2014, 16:29 #3 New Member   sebastien vilfayeau Join Date: Feb 2012 Posts: 11 Rep Power: 6 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

 October 23, 2014, 08:58 #4 New Member   Join Date: Feb 2013 Posts: 18 Rep Power: 5 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.

July 9, 2016, 04:58
#5
Senior Member

Ehsan Asgari
Join Date: Apr 2010
Posts: 304
Rep Power: 9
Quote:
 Originally Posted by Shahr 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.
Hi,

Did you find a way to calculate TKE dissipation?!

Thanks

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post nedved OpenFOAM Running, Solving & CFD 15 Yesterday 03:40 eelcovv OpenFOAM 0 June 8, 2010 11:35 blackbody Main CFD Forum 1 May 12, 2010 18:54 laurencep OpenFOAM 2 April 22, 2010 04:53 nedved OpenFOAM Running, Solving & CFD 1 November 25, 2008 21:21

All times are GMT -4. The time now is 19:16.