[cfdengineering]

Sorry, but I can't find anywhere a default set of values for the compressible realizable k-epsilon model:

Cmu
A0
C2
alphak
alphaEps
alphah

can anybody help me?
thanks

[wikstrom]

From paper by Shih et al. (Computers and Fluids Vol. 24, No. 3, pp. 227-238, 1995) it seems to be


realizableKECoeffs
{
Cmu Cmu [0 0 0 0 0 0 0] 0.09;
A0 C1 [0 0 0 0 0 0 0] 4.0;
C2 C2 [0 0 0 0 0 0 0] 1.92;
alphak alphaK [0 0 0 0 0 0 0] 1.0;
alphaEps alphaEps [0 0 0 0 0 0 0] 1.2;

}

/N

[stefanke]

Seems like there are some missing entries like alphah etc.

Does anybody know the realiableKECoeff ?

I cannot find any references in OF?

[hjasak]

realizableKECoeffs
{
Cmu Cmu [0 0 0 0 0 0 0] 0.09;
A0 A0 [0 0 0 0 0 0 0] 4.04;
C2 C2 [0 0 0 0 0 0 0] 1.92;
alphak alphak [0 0 0 0 0 0 0] 1.0;
alphaEps alphaEps [0 0 0 0 0 0 0] 0.76923;
}

[stefanke]

thanks Hrv, but with this setup the following error occurs:

keyword alphah is undefined in dictionary "
in turbulenceProperties::realizableKECoeffs"

[pierre]

the coefficient alphah is used to evaluate the effective turbulent thermal diffusivity. (see realizableKE.h)

just add alphah alphah [0 0 0 0 0 0 0] 1;

as in

realizableKECoeffs
{
Cmu Cmu [0 0 0 0 0 0 0] 0.09;
A0 A0 [0 0 0 0 0 0 0] 4.04;
C2 C2 [0 0 0 0 0 0 0] 1.92;
alphak alphak [0 0 0 0 0 0 0] 1.0;
alphaEps alphaEps [0 0 0 0 0 0 0] 0.76923;
alphah alphah [0 0 0 0 0 0 0] 1;
}

[sylvester]

I have a question about the relationship between the value of sigmaEps given by Shih (1.2) and the value of alphaEps given by Jasak (0.76923).
With these values alphaEps = 1 / (sigmaEps + 0.1), but where does the 0.1 come from?
I have studied the equations in the Shih paper and realizable.C, but there is too much mathematical wizardry going on for me to fully understand it.

Thank you.
Sylvester

[sradl]

Dear Foamers,

to clarify the situation the following should be noted:

OpenFOAM's implementation of the realizable k-e model does not strictly follow the paper of Shih et al. and the coefficients proposed in it:

sigmaEps is 1.3 in OF (and hence 1/sigmaEps = alphaEps = 0.76923), whereas Shih et al. [1] propose sigmaEps = 1.20 (see Eqn. 28 of their paper). Furthermore, OF uses C2=1.92 whereas Shih et al. [1] use 1.9 (see table 2 of their paper). These two deviations may be errors or may be introduced by the programmers/users to be consistent with the standard k-e model.

Also A0 is 4.0 in Shih et al. [1] and not 4.04 as proposed here. (However, the value of 4.04 is consistent with www.cfd-online.com/Wiki while the others are not).

It seems that all equations are consistent with the paper of Shih et al. [1] except the fact, that OF uses (nut/sigmak+nu) and (nut/sigmaEps+nu) instead of (nut/sigmak) and (nut/sigmaEps) as in the paper of Shih et al. [1] respectively. This is of course a small effect and should not have any further consequences at high Re-number flows.

I hope this clarifies the parameters of the OF realizableKE model and I would like to suggest to include a clarification in the next release of OF.

Reference:
[1]Tsan-Hsing Shih, William W. Liou, Aamir Shabbir, Zhigang Tang and Jiang Zhu. 1995. A New k-epsilon Eddy Viscosity Model for High Reynolds Number Turbulent Flows, Computers and Fluids 24. 227-238.

[vaina74]

Hi, foamers.

I have two question about realizable k-epsilon turbulent model. I included in RASProperties file the following coefficients (I found them in realizableKE.H):

realizableKECoeffs
{
    Cmu         0.09;
    A0          4.0;
    C2          1.9;
    alphak      1.0;
    alphaEps    0.833333;
    alphah      1.0;    // only for compressible
}

What is the difference from Mr Hjasak (respect!) suggested ones?
Anyway, I obtain the following error:

Selecting incompressible transport model Newtonian
Selecting RAS turbulence model realizableKE
[0] 
[0] 
[0] LHS and RHS of + have different dimensions
     dimensions : [0 0 -1 0 0 0 0] + [0 2 -3 0 0 0 0]
[0] 
[0] 
[0]     From function operator+(const dimensionSet& ds1, const dimensionSet& ds2)
[0]     in file dimensionSet/dimensionSet.C at line 403.
[0] 
FOAM parallel run aborting

What does it mean?
Thanks for your attention.

[vaina74]

It means I'm an idiot. The realizableKE coefficients are correct, but I derived /0/epsilon from /0/omega (it was an 'old' case) and I forgot to edit the units too.