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-   -   omegaWallFunction implementation (http://www.cfd-online.com/Forums/openfoam/115937-omegawallfunction-implementation.html)

Horus April 9, 2013 13:37

omegaWallFunction implementation
 
Hello,

I'm studying the implementation of the incompressible omegaWallFunction.

http://foam.sourceforge.net/docs/cpp/a09165_source.html

Code:

00207        scalar omegaVis = 6.0*nuw[faceI]/(beta1_*sqr(y[faceI]));
00208
00209        scalar omegaLog = sqrt(k[faceCellI])/(Cmu25*kappa_*y[faceI]);
00210
00211        omega[faceCellI] = sqrt(sqr(omegaVis) + sqr(omegaLog));

\omega = \sqrt{\omega_{vis}^2 + \omega_{log}^2}
\omega_{vis} = \frac{6 \nu}{\beta_1 \cdot y^2}
\omega_{log} = \frac{k}{\sqrt[4]{C_\mu} \cdot \kappa \cdot y}

This clearly becomes oo when y approaches 0. Does this account for the turbulence damping near the wall?

Next question: What is G?

Code:

00173    volScalarField& G =
00174        const_cast<volScalarField&>
00175        (
00176            db().lookupObject<volScalarField>
00177            (
00178                turbulence.type() + ".G"
00179            )
00180        );

And set here:

Code:

00213        G[faceCellI] =
00214            (nutw[faceI] + nuw[faceI])
00215            *magGradUw[faceI]
00216            *Cmu25*sqrt(k[faceCellI])
00217            /(kappa_*y[faceI]);
00218    }

The paper mentioned in the source code is available nowhere...

I'm especially clueless that the last part with the G is about?

Thanks!
Florian

fumiya April 9, 2013 18:08

Hi Florian,

For the second question, the followings will be of help:
The term G is the production of turbulent kinetic energy.

Hope this helps,
Fumiya

dancfd April 28, 2014 21:10

Hello all,

I noticed that the logarithmic component of omega1 in the code is not representative of the Menter 2001 paper.

The code is:
Code:

scalar omegaLog = sqrt(k[faceCellI])/(Cmu25*kappa_*y[faceI]);
Which gives:
\omega_{log} = \frac{\sqrt{k}}{\sqrt[4]{C_\mu} \kappa y}

Menter 2001 gives:
\omega_{log} = \frac{u_\tau}{\sqrt[4]{C_\mu} \kappa y}
Where C_mu = 0.09.

Why the difference? A message above makes reference to the following website: http://www.cfd-online.com/Wiki/Two_e...bulence_models

The last term of the last equation in the "Standard Wall Functions" section at that link matches the code, but it is still not clear why the code chose the equation that was selected (Wilcox 1994 eq 6.84) and not that which was defined in Menter 2001.

Does anyone know why the code is what it is, and not in line with Menter 2001?

Thanks,

Daniel


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