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February 10, 2011, 07:13 
Inconsistency in LaunderSharma ke model?

#1 
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 366
Rep Power: 12 
Hi all, actually I'm not sure if this is a real bug or not, but I have some questions about the LaunderSharma model implementation in OpenFOAM (1.6). The literature about this model tells me that, in order to avoid a singular behavior of the sink term in the epsilon equation, the epsilon itself could be replaced with a quantity called epsilonTilda, which is equal to:
epsilonTilda=epsilon2*nu*magSqr(grad(sqrt(k)) Well, looking at the source code, it seems like the epsilon equation is solved for epsilonTilda, and after that the "corrected" epsilon (epsilonTilda + 2*nu*...) is used as a sink term for the kequation. However, in all other formulas or equations where epsilon is needed (in particular the turbulent eddy viscosity formula and the calculation of Ret for the damping functions), epsilonTilda is used instead...Maybe I'm missing something, but this sounds not so consistent to me as, in general, epsilon and epsilonTilda are not the same. Can anybody correct me or give some explanation for this? Thank you all V. 

February 11, 2011, 06:48 

#2 
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 366
Rep Power: 12 
So, no one's got an answer?


February 15, 2011, 05:37 

#3 
Senior Member
Paulo Vatavuk
Join Date: Mar 2009
Location: Campinas, Brasil
Posts: 158
Rep Power: 10 
Hi vkrastev,
I haven't studied the OpenFOAM implementation yet, but the original model has in fact this apparent inconsistency that you mentioned. Since the extra term is expected to be zero everywhere, except near the wall, epsilon and epsilonTilda will be almost equal, so there should be no problem in using one instead of the other. 

February 15, 2011, 06:42 

#4  
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 366
Rep Power: 12 
Quote:
V. 

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