# Understanding k-omega SST model source code

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 September 8, 2009, 04:45 Understanding k-omega SST model source code #1 New Member   Tomi Honkanen Join Date: Sep 2009 Location: Finland Posts: 1 Rep Power: 0 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 K-omega 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 Two-Equation 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...nter-SST-paper [3] K-omega SST in OpenFOAM-1.5 http://www.tfd.chalmers.se/~hani/kur...lenceModel.pdf [4] http://www.cfd-online.com/Wiki/SST_k-omega_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 omega-equation, 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 G-term 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 G-term 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, 07:33 #2 Member   Marco Müller Join Date: Mar 2009 Location: Germany Posts: 94 Rep Power: 17