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March 24, 2014, 13:40 
Dissipation calculation in LES  Isotropic turbulence

#1 
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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 strainrate 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 

March 24, 2014, 13:49 

#2  
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Filippo Maria Denaro
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Quote:
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. 

March 25, 2014, 14:18 

#3 
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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? 

March 25, 2014, 16:33 

#4 
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Filippo Maria Denaro
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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 ... 

Tags 
dissipation, isotropic turbulence, les 
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