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September 8, 2009, 05:45 
Understanding komega SST model source code

#1 
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Tomi Honkanen
Join Date: Sep 2009
Location: Finland
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Hi,
I'm currently working on my master's thesis and using OpenFOAM 1.5 for aerodynamics calculations (incompressible, subsonic). I was writing down equations used by the Komega SST turbulence model implemented in OF1.5, when I run into some difficulties. I hope someone could shed some light into this. The source code of the model clearly states that the implementation is based on this paper: Menter, F., Esch, T. "Elements of Industrial Heat Transfer Prediction" 16th Brazilian Congress of Mechanical Engineering (COBEM), Nov. 2001 I do not have that, but instead I have looked at the following sources: [1] Menter SST TwoEquation Model from 2003 http://turbmodels.larc.nasa.gov/sst.html [2] Ten Years of Industrial Experience with the SST Turbulence Model http://cfd.mace.manchester.ac.uk/flo...nterSSTpaper [3] Komega SST in OpenFOAM1.5 http://www.tfd.chalmers.se/~hani/kur...lenceModel.pdf [4] http://www.cfdonline.com/Wiki/SST_komega_model My questions are: 1) In the source code KOmegaSST.C on line 397 nut is defined as: nut_ = a1_*k_/max(a1_*omega_, F2()*sqrt(S2)); and on line 344: S2 = magSqr(symm(fvc::grad(U_))); However on line 363 in the omegaequation, the term gamma*S^2 is stated as gamma(F1)*2*S2 Now where does that factor 2 between gamma and S^2 come from? In Ref [1] it is found that for the 2003 model in fact this formulation would be correct (S=sqrt(2*S_ij*S_ij)), if this was used then the nut equation is inconsistent as the sqrt(2) factor is missing! 2) The Gterm defined in line 345 is nut_*2*S2 As far as I understand it is not defined like this in Refs [1,2,3,4]. How is this done in the code when Gterm is used in the same way as in Refs? I suppose there is nothing wrong with the code, and just some programming gimmick is used that I don't understand, but it would be much appreciated if someone could help me to see how the model was implemented. 

September 8, 2009, 08:33 

#2 
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Marco Müller
Join Date: Mar 2009
Location: Germany
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