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May 9, 2016, 11:37 
omega wilcox definition

#1 
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I'm using komega SST model in LowRe 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? 

May 11, 2016, 17:13 

#2 
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Clara
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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! 

May 11, 2016, 18:37 

#3 
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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?


May 11, 2016, 18:48 

#4 
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Clara
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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! =) 

May 12, 2016, 07:11 

#5 
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Sorry i haven't understood well what i have to do to obtain near wall distance.


May 12, 2016, 12:27 

#6 
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Clara
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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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