# how to reduce y+

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 January 16, 2003, 13:06 how to reduce y+ #1 Cindy Jones Guest   Posts: n/a Hi, everyone Well,I guess my question is a stpid one. I had a very simple test model. It was just a pipe with an elbow. I kept adapting the grids, but the Max y+ was still way to high (>300). Can anyone tell me how important the y+ value is and how to solve this problem? By the way the pipe's diameter is just 1m and Re is about 10^5 I also heard about the first grid should be outside the boundary layer? How can I check this? Many thanks Cindy

 January 17, 2003, 13:50 Re: how to reduce y+ #2 Ray Guest   Posts: n/a Your y+ value depends on a variety of conditions such as flow speed. YOu need to look at which turbulence model you are using and what kind of wall treatment you are using. Try creating a new mesh and use a boundary layer on the wall just to see what kind of y+ you get. Y+ will also change if it has not reached a steady state solution. Ray

 January 17, 2003, 23:12 Re: how to reduce y+ #3 zhhuang Guest   Posts: n/a Cindy, yeah!If u use the wall function the y+ should be between the 30-200,if u use the 2-layer model,Y+ should 1-5,the y distance can be determined by the fluent training document.use emperical formula get the Cf,then Ut,after that,the Yp you can get.Then you can mesh your grid with this Yp. zhhuang

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