# Problem calculate Y in compressible turbulence model

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 May 31, 2006, 11:00 Hi all, May be It's a studp #1 Member   Luca M. Join Date: Mar 2009 Location: Luzern, Switzerland Posts: 59 Rep Power: 9 Hi all, May be It's a studpid question but I've noticed in file "turbulence.C" in compressible turbulence models that OF calucalte Y+ like: Yp = pow(Cmu.value(), 0.25) *y_[patchNo] *sqrt(k()().boundaryField()[patchNo].patchInternalField()) /( mu().boundaryField()[patchNo].patchInternalField() *rho_.boundaryField()[patchNo]<--- ); I think that it's wrong because I need the Kinematic viscosity that is defined as mu/rho. (I think that mu is refereed to Dynamic viscosity) and so the right way to calculate Y+ is Yp = pow(Cmu.value(), 0.25) *y_[patchNo] *sqrt(k()().boundaryField()[patchNo].patchInternalField()) /( mu().boundaryField()[patchNo].patchInternalField() /rho_.boundaryField()[patchNo]<--- ); I'm wrong ?! Luca

 May 31, 2006, 11:41 Hi, In the calculation of Y #2 Member   Pierre Le Fur Join Date: Mar 2009 Location: UK Posts: 60 Rep Power: 9 Hi, In the calculation of Yplus in wallViscosity.H and WallFunctions.H for compressible flow codes, it is written: " scalar yPlus = Cmu25*turbulenceModel::y_[patchi][facei]*sqrt(k_[faceCelli]) /(muw[facei]/rhow[facei]); " which is as you suggest, so I guess you might be right. Thought that member function defined in turbulence.C is not used anywhere it seems. Pierre

 May 31, 2006, 11:58 Hi Pierre, So It's a bug.. #3 Member   Luca M. Join Date: Mar 2009 Location: Luzern, Switzerland Posts: 59 Rep Power: 9 Hi Pierre, So It's a bug.. I use the function Yp in turbulence.C to check y+ for compressible turbulence model that I use. In detail I build the utility starting from "checkYPlus" incompressible utility where, I think, it uses Yp function. So how do you suggest me to build my utility to check y+ without Yp function in turbulence compressible model?! Thanks in advance Luca

 May 31, 2006, 12:19 why don't you calculate Yplus #4 Member   Pierre Le Fur Join Date: Mar 2009 Location: UK Posts: 60 Rep Power: 9 why don't you calculate Yplus directly as you wrote it above without using Yp function? Pierre

 June 1, 2006, 05:16 Thanks Luca, it was a bug and #5 Super Moderator   Mattijs Janssens Join Date: Mar 2009 Posts: 1,416 Rep Power: 17 Thanks Luca, it was a bug and has been fixed. Any more of these? If so please report them on the bugs list so we can keep track.

 June 1, 2006, 05:53 Ok,Mattijs!! Thanks for the #6 Member   Luca M. Join Date: Mar 2009 Location: Luzern, Switzerland Posts: 59 Rep Power: 9 Ok,Mattijs!! Thanks for the suggestion, and support. Luca

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