# How to decide Y plus

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 August 10, 2012, 13:23 How to decide Y plus #1 New Member   prashant kadam Join Date: Dec 2009 Location: Pune Posts: 10 Rep Power: 7 Hello All, I have question how to decide the y plus? __________________ regards, Prashant

 August 10, 2012, 13:50 #2 Administrator     Peter Jones Join Date: Jan 2009 Posts: 669 Rep Power: 10 You should check CFD-Wiki and the online tools we have here at CFD Online: Here is a tool to compute the needed wall distance for a desired y-plus: http://www.cfd-online.com/Tools/yplus.php Here are the formulas used: http://www.cfd-online.com/Wiki/Y_plu...nce_estimation Here is the definition of y plus: http://www.cfd-online.com/Wiki/Dimen...e_%28y_plus%29

 August 12, 2012, 02:52 #3 New Member   prashant kadam Join Date: Dec 2009 Location: Pune Posts: 10 Rep Power: 7 Thanks for your reply, I have done the calculations by using the formulas which you have suggested. But I don't know how to choose the y plus for the calculation of the first cell height. My mass flow is 0.055 m/s for air. By calculation i got Re=52401, Rho=1.18415, but when I take the y plus value 80 then the first cell height is 4.37 mm.. But wb=hen i take y plus = 1 then first cell height is 0.055 mm. is that correct. One more question, On which basis we can select the y plus value for the calculation of the first cell height. As per my study y plus between 1-3 is viscous sub-layer or laminar region , 3-30 transition layer, and 30-120 or 150 is turbulent layer. but on which basis should i choose the y plus value. when Reynolds no is more boundary layer is small. then the region is viscous sub-lyer near the wall. __________________ regards, Prashant

 August 12, 2012, 03:29 #4 Administrator     Peter Jones Join Date: Jan 2009 Posts: 669 Rep Power: 10 What y plus you want depends on what turbulence model you use.

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