Dear respected Fluent users, could you please inform me about how to get the dimesionless wall distance value Y+. Is there a macro in Fluent to get it directly. Thanks in advance Wael

Do you need to get it in a UDF?

If so use F_STORAGE_R(f,tf,SV_WALL_YPLUS_UTAU) where f and tf are face index and thread repectively

Or if you're just looking for the values, you can see them using Display->Contours (or Plot->XY Plot, or Report->Surface Integrals, etc.)... y+ values are available under "Turbulence"

Hope this helps, and good luck, Jason

Daer Alec Eiffel and Jason, Thank you very much. Yes I want to use Y+ in UDF for a low Re K-e turbulence model. I have to use the value in equauation like -------- real f_mu(cell_t c, Thread *t) { return 1.-pow(1+abs((1-n)/(1+n))*SV_WALL_YPLUS_UTAU(c,t),2),........;} ------------ Can I use it in this way? Thanks for your help Wael

it cant be used in that way. you fist need to get the face index and thread for the boundary faces that you would let to get the y+ value for. Then store the y+ in a variable. You will need something like

real y_plus;

y_plus = F_STORAGE_R(f,tf,SV_WALL_YPLUS_UTAU);

return 1.-pow(1+abs((1-n)/(1+n))*y_plus,2)

Thanks a lot Mr Alec Eiffel for your concern and valuable information. I want to use Y+ values in the fluid zone for each cell every iteration. As you know the k-e model equations and the turbulent viscocity will use Y+ via f_mu . Could you please inform me how I can define the index and thread (like Thread *t; and cell_t c; !) . This is the 1st time for me to use the F_STORAGE..... Thanks in advance and my best regards. Wael

Wall y+ is only available at wall boundaries. It has a value of zero at all internal cells in the fluid zone. If you display contours of y+ on any model you will notice that it only has a value in cells adajacent to wall boundaries.

Dear Mr Alec Eiffel, You are absolutly right.In the model I want use (Nagano-Hishida 1987) Y+ is defined as Y+=Utau*y/nu and it is used anywhere in the fluid domain. So, now I have to use that equation to calculate Y+ not the value of Fluent (IS THAT RIGHT?). If so, the peoblem will be in Utau=sqrt(Tau_wall/roh), I do not know how to get Tau_wall from Fluent. Please advise. Your help is appreciated too much. My best regards. Wael