# what is correct boundary condition for K-w sst model at y+<1?

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 August 4, 2013, 14:35 what is correct boundary condition for K-w sst model at y+<1? #1 Senior Member   Join Date: Jun 2011 Posts: 153 Rep Power: 8 Hi I found some thread about k-w sst boundary conditions unfortunately they are not clear in low y+ please let me know what is correct boundary conditions for k, w and nut for y+<5 Best Regards

 August 4, 2013, 15:42 #2 New Member   Andre Weiner Join Date: Aug 2012 Posts: 29 Rep Power: 7 Hello! omega: Menter's automatic wall funcion works for all parts of the momentum boundary layer, in openfoam it's the omegaWallFunction http://www.cfd-online.com/Wiki/Near-...k-omega_models or you use the solution for the viscos sublayer to set the boundary value http://turbmodels.larc.nasa.gov/sst.html (there is an equation for omega_wall) for y^+<5 both give the same results k: fixed value 0 or zero gradient if you look at same results for k near the wall (from other simulations for example), you will see that both are valid (again for y^+<5) nut: calculated or fixed value 0 or nutLowReWallFunction (sets the value to zero and provides a function for calculating y^+ which is needed for the yPlusRAS tool) This is what i tried so far and it worked for mi :-) Best regards, Andre

August 5, 2013, 03:51
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 Originally Posted by andre.weiner Hello! nut: calculated or fixed value 0 or nutLowReWallFunction (sets the value to zero and provides a function for calculating y^+ which is needed for the yPlusRAS tool) This is what i tried so far and it worked for mi :-) Best regards, Andre

what function should be set for calculating y+ ? and how set it ?
can you attached an example for k,w,nut (initial file at folder 0)?

Best Regards

 August 5, 2013, 10:29 #4 Senior Member   Joachim Join Date: Mar 2012 Location: Providence, RI Posts: 143 Rep Power: 8 Actually, I think that nutLowReWallFunction is a wall function for low-Re turbulence models. If you use LaunderSharmaKE and have y+ ~ 60, you can use it for example. Also, try using 1e-9 (or any small value) rather than 0 when imposing the BC. Good luck!

 August 5, 2013, 14:17 #5 New Member   Andre Weiner Join Date: Aug 2012 Posts: 29 Rep Power: 7 for k: Code: ``` myWall { type zeroGradient; } // or myWall { type fixedValue; value uniform 0; }``` for omega: Code: ``` myWall { type omegaWallFunction; }``` for nut: Code: ``` myWall { type fixedValue; value uniform 0; } // or myWall { type calculated; value uniform 0; // optional value entry } // what i prefer myPatch { type nutLowReWallFunction; }``` I don't know for what the nutLowReWallFunction schould or schloud not be, but if you take little look at the code: it sets nut to zero: Code: ```tmp nutLowReWallFunctionFvPatchScalarField::calcNut() const { return tmp(new scalarField(patch().size(), 0.0)); }``` and provides a function for y+: Code: ```tmp nutLowReWallFunctionFvPatchScalarField::yPlus() const { .... return y*sqrt(nuw*mag(Uw.snGrad()))/nuw; }``` Regards, Andre Tauseef likes this.

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