[Hillie]

Dear Foamers.

I am trying to understand the implementation of the omegawallfunction.

In the code the following paper is referenced: Menter, F., Esch, T.
"Elements of Industrial Heat Transfer Prediction"
16th Brazilian Congress of Mechanical Engineering (COBEM),
Nov. 2001

As has been posted on this forum, on a couple of places, the paper is kinda lost. Therefore I though I would open a new thread.

The main thing which I am having issues with understanding is the scaling of omega with wall distance.

In the paper by Wilcox (Reassessment of the scale-determining equation for advanced turbulence models) he describes the scaling of omega in equations 30 and 32.
In equation 30 describes a scaling of 1/y of omega in the log layer. for y+ -> Wilcox describes the scaling of Omega as 1/y^2.

Now if I look at the source code, log layer omega scales as 1/y but the viscous omega scales as 1/sqrt(y) instead of 1/y^2.

scalar omegaVis = 6.0*nuw[faceI]/(beta1_*sqr(y[faceI]));

scalar omegaLog = sqrt(k[cellI])/(Cmu25*kappa_*y[faceI]);

Can anybody explain me why this is implemented like this?

Cheers

[giammy92]

I agree with you Hillbert, in fact i have just performed a simulation on a very fine mesh (y+ about 1 or less) with k-omega SST and using omegaWallFunction i don't achieve good results according experimental data. I have best results when i use omega= 1e7 for wall, that is an estimate of Menter's wall boundary condition. So i think that omegaWallFunction calculates a wrong value of omega viscous.

[Hillie]

hi, giammy92

I am also using a constant omega boundary condition, since that gives me better results.
I am still finding it a bit weird though. Once the flow goes into the viscous sublayer the value for omega should behave according to wilcox his equation, which is exactly the equation implemented apart from the 1/sqrt(y) instead of 1/y^2 term.

[giammy92]

omega viscous depends from 1/y^2 that is sqr(y) and not sqrt(y) then the implementation of omega viscous in OF is corrected but gives me worse results comparated with omega fixedValue 1e7

[giammy92]

the only difference that i note is that in Wilcox's omega forumula y is the first cell center, while in OF we have y of first face