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-   -   Understanding k-omega SST model source code (http://www.cfd-online.com/Forums/openfoam-programming-development/68128-understanding-k-omega-sst-model-source-code.html)

tmhonka September 8, 2009 04:45

Understanding k-omega SST model source code
 
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.



marico September 8, 2009 07:33

http://www.cfd-online.com/Forums/ope...komegasst.html


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