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Old   May 9, 2016, 11:37
Default omega wilcox definition
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I'm using k-omega SST model in Low-Re mode so without wall functions.
I set omega with fixedValue calculated with wilcox's formula:

omega = 6*nu/(0.075*y^2)

in which y should be the first cell center nearest to wall. How i can calcaulate this? Is there an utility for this?
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Old   May 11, 2016, 17:13
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Dear giammy92,

What do you need to calculate? y or omega? or you want to calculate omega within the code directly?

Cheers!
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Old   May 11, 2016, 18:37
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Hi risku9, I want calculate omega with wilcox formula at wall because I think that is more accurated compared to omegaWallFunction. I need to know y in formula that should be the first cell center right? Is there an utility to calculate it?
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Old   May 11, 2016, 18:48
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Hey!

If what you want to get is y, I think you can find it in the wall function definition of omegaWallfunction:

src/turbulenceModels/incompressible/RAS/derivedFvPatchFields/wallFunctions/omegaWallFunctions/omegaWallFunctions

You can find this piece of code:

const scalarField& y = turbulence.y()[patchI];

Which I believe refers to the nearWall distance, as if you look into the C++ documentation of OpenFOAM:

http://openfoam.github.io/Documentat...ml/a01744.html

Looking for turbulenceModel::y() and clicking on it you will reach:
http://openfoam.github.io/Documentat...ce.html#l00157

where it explains:

//- Return the near wall distances
158 const nearWallDist& y() const
159 {
160 return y_;
161 }

So I think if you use that turbulence.y() as in the omegaWallFunction now, you should be able to get to do what you would like!

I hope this helps! =)
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Old   May 12, 2016, 07:11
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Sorry i haven't understood well what i have to do to obtain near wall distance.
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Old   May 12, 2016, 12:27
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Hey,

So I think you would just need to create a new wall function, in which you set that omega to the value you want. I was checking the original OmegaWallFunction in the code in the folder of installation of openfoam:

OpenFOAM/src/turbulenceModels/incompressible/RAS/derivedFvPatchFields/wallFunctions/omegaWallFunctions/

And it is almost already what you are looking for as beta1_ = 0.075, you would just need to comment the omegaLog component.
If look in line 234 from omegaWallFunction.C file:

// Set omega and G
forAll(nutw, faceI)
{
label cellI = patch.faceCells()[faceI];

scalar w = cornerWeights[faceI];

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

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

omega[cellI] += w*sqrt(sqr(omegaVis) + sqr(omegaLog));

G[cellI] +=
w
*(nutw[faceI] + nuw[faceI])
*magGradUw[faceI]
*Cmu25*sqrt(k[cellI])
/(kappa_*y[faceI]);
}
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