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MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?

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Old   October 4, 2005, 03:32
Default MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?
  #1
Wael
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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
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Old   October 4, 2005, 07:06
Default Re: MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?
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Alec Eiffel
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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
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Old   October 4, 2005, 08:32
Default Re: MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?
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Jason
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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
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Old   October 4, 2005, 22:03
Default Re: MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?
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Wael
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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
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Old   October 5, 2005, 07:37
Default Re: MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?
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Alec Eiffel
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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)
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Old   October 5, 2005, 12:52
Default Re: MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?
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Wael
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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
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Old   October 5, 2005, 13:04
Default Re: MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?
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Alec Eiffel
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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.
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Old   October 6, 2005, 04:24
Default Re: MACRO FOR DIMENSIONLESS WALL DISTANCE Y+ ?
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Wael
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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
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