CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Dissipation calculation in LES - Isotropic turbulence

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

Like Tree1Likes
  • 1 Post By FMDenaro

Reply
 
LinkBack Thread Tools Display Modes
Old   March 24, 2014, 13:40
Default Dissipation calculation in LES - Isotropic turbulence
  #1
Member
 
Join Date: Jul 2010
Posts: 36
Rep Power: 7
MaryBau is on a distinguished road
Hi everyone;

I am 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), so the flow behaviour is correct. However if I calculate epsilon directly from the filtered velocity field it does not give me the correct value. I do not think is a coding error, probably my formulation of epsilon is not correct. I am calculating my total dissipation (modelled + resolved) as:

epsilon=2*(nu+nuSgs)*(S::S) where S is the strain-rate

Is this valid for decaying isotropic turbulence? 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
File Type: pdf calculatedEdt.pdf (23.3 KB, 24 views)
MaryBau is offline   Reply With Quote

Old   March 24, 2014, 13:49
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 1,651
Rep Power: 23
FMDenaro will become famous soon enough
Quote:
Originally Posted by MaryBau View Post
Hi everyone;

I am 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), so the flow behaviour is correct. However if I calculate epsilon directly from the filtered velocity field it does not give me the correct value. I do not think is a coding error, probably my formulation of epsilon is not correct. I am calculating my total dissipation (modelled + resolved) as:

epsilon=2*(nu+nuSgs)*(S::S) where S is the strain-rate

Is this valid for decaying isotropic turbulence? 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

of course the expression for dissipation does not depend on the type of flow, it must be general...
Said that, if you assume no production of energy, the balance dE/dt=-epsilon must be true even at the initial condition but that does not hold from your figure.
FMDenaro is offline   Reply With Quote

Old   March 25, 2014, 14:18
Default
  #3
Member
 
Join Date: Jul 2010
Posts: 36
Rep Power: 7
MaryBau is on a distinguished road
Thanks Filippo, what I ment to say is if my expression for the dissipation is correct?

epsilon=2*(nu+nuSgs)*(S::S)

or what could it be the reason for this discrepancy in my results?
MaryBau is offline   Reply With Quote

Old   March 25, 2014, 16:33
Default
  #4
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 1,651
Rep Power: 23
FMDenaro will become famous soon enough
the expression of the total dissipation you wrote is correct, of course coding it can have some errors...

Anyway, check a t=0 both dE/dt and the dissipation ...
MaryBau likes this.
FMDenaro is offline   Reply With Quote

Reply

Tags
dissipation, isotropic turbulence, les

Thread Tools
Display Modes

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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Default inlet turbulence for LES N Barton CFX 11 July 24, 2015 00:34
LES calculation of EPSILON (turbulence dissipation) Gosi OpenFOAM Post-Processing 3 October 23, 2014 08:58
Calculation of initial k for RAS turbulence models shipman OpenFOAM 1 August 28, 2013 03:52
Warning 097- AB CD-adapco 6 November 15, 2004 05:41
calculation of (turbulent) dissipation energy ? max Main CFD Forum 3 August 18, 1999 09:42


All times are GMT -4. The time now is 22:02.