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-   -   RealizableKE (http://www.cfd-online.com/Forums/openfoam-solving/58744-realizableke.html)

cfdengineering November 7, 2005 06:11

Sorry, but I can't find anywhe
 
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 November 11, 2005 04:41

From paper by Shih et al. (Com
 
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 August 14, 2006 11:49

Seems like there are some miss
 
Seems like there are some missing entries like alphah etc.

Does anybody know the realiableKECoeff ?

I cannot find any references in OF?

hjasak August 14, 2006 11:51

realizableKECoeffs { Cmu
 
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 August 14, 2006 11:56

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

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

pierre August 14, 2006 12:40

the coefficient alphah is used
 
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 August 29, 2007 03:13

I have a question about the re
 
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 July 12, 2008 12:13

Dear Foamers, to clarify th
 
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 March 28, 2011 16:09

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):
Code:

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:
Code:

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 March 31, 2011 03:45

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.


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