# bluff body and Y+

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 April 25, 2006, 13:13 bluff body and Y+ #1 justin Guest   Posts: n/a Hi,everyone. I am studying wind environment around buildings. The problem is how to easily set the first cells aroud the bluff body to make the y+ at the desirable range (30~60). As the pressure and stress on the surfaces are variable, that means the first cells should be different. Now I used the structured mesh. After convergence, the range of y+ on the suface was from 40 ~ 1000. If I use y+ grid adaption, the range of y+ droped down slowly ( once about half decrease)and every convergence spend a long time. Do you have any strategies or suggestions? Thanks in advance Justin

 April 26, 2006, 10:07 Re: bluff body and Y+ #2 Chandra Murthy Guest   Posts: n/a y+ will be very important parameter to look in, when it is required to model heat tranfer to the walls or to capture the boundary layer very accurately. in your case (wind environment around building), does it required to control the y+ in such a close manner. Otherwise, if there is something else, write it.

 April 26, 2006, 11:08 Re: bluff body and Y+ #3 justin Guest   Posts: n/a thanks for your reply. But I still don't know how to make this value around bluff body pefect in Fluent. the range of the value is too large to control easily. sometimes the lower is above than 30, but after adaption, part of the values will be lower than 30. I heard that y+ in CFX can be defined and you don't worry the mesh density leads to the y+ less than 30. It looks like fluent doesn't have this function. This problem cost me a long time. Now I am so disappointed. please help!!!

 May 4, 2006, 20:13 Re: bluff body and Y+ #4 Naresh Guest   Posts: n/a hi I had this Problem too. Just try with boundry layer, and type firstat "first row a" =2. U will see what happened in the near of the wall, if u click the wall line. Just try. abhay

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