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-   -   kOmegaSSTSAS implementation in OF 2.1 (http://www.cfd-online.com/Forums/openfoam-bugs/101754-komegasstsas-implementation-2-1-a.html)

RealSoutherner May 13, 2012 11:48

kOmegaSSTSAS implementation in OF 2.1
 
Hello,

I think there are errors in the implementation of the kOmegaSSTSAS model in OF 2.1, but I'm not certain.

Firstly, the production term G differs from the kOmegaSST model and the basic kOmega model, where I believe they should be consistent. OF 1.6 has a consistent formulation in all 3.

In kOmegaSSTSAS(OF2.1):
S2 = 2*magSqr(symm(fvc::grad(U)));
G = nuSgs*0.5*S2;
nuSgs = a1*k/max(a1*omega, F2()*sqrt(S2));

In kOmegaSST(OF2.1):
S2 = 2*magSqr(symm(fvc::grad(U)));
G = nut*S2;
nut = a1*k/max(a1*omega, F2()*sqrt(S2));

So, G is half the magnitude in the kOmegaSSTSAS model. I can't find anywhere in the literature where this is true, but maybe someone knows. I have tested both formulations on a turbulent channel flow and actually see a slightly better result with the new "wrong" formulation, which makes me question the wrongness.

Secondly, the related term in the omega equation is given as gamma(F1)*0.5*S2. This is how it's shown in Menter et al (Ten Years of Industrial Experience with the SST Turbulence Model, 2003) but in Menter et al (The SST Turbulence Model with Improved Wall Treatment..., 2003) it is given (using OF variables) as gamma(F1)*G/nut. Furthermore, at http://turbmodels.larc.nasa.gov/sst.html, the formulation that OF uses is said to be an error in the original paper. This also affects the kOmegaSST model in OF.

Hopefully someone can confirm these errors or knows where in the literature these modifications have been made. Thanks.

Tarak August 17, 2012 01:31

Hii,

This was a bug in OF and has been rectified through mantis bugtracker with ID 0000575 (you can see the edited version in the git repository). This reduced production term was leading to a spurious reduction of turbulent viscosity.


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