How to decide Y plus
Hello All,
I have question how to decide the y plus? 
You should check CFDWiki and the online tools we have here at CFD Online:
Here is a tool to compute the needed wall distance for a desired yplus: http://www.cfdonline.com/Tools/yplus.php Here are the formulas used: http://www.cfdonline.com/Wiki/Y_plu...nce_estimation Here is the definition of y plus: http://www.cfdonline.com/Wiki/Dimen...e_%28y_plus%29 
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 13 is viscous sublayer or laminar region , 330 transition layer, and 30120 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 sublyer near the wall. 
What y plus you want depends on what turbulence model you use.

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