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Old   August 10, 2012, 14:23
Default How to decide Y plus
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prashant kadam
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Hello All,

I have question how to decide the y plus?
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Old   August 10, 2012, 14:50
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Peter Jones
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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
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Old   August 12, 2012, 03:52
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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.
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Old   August 12, 2012, 04:29
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What y plus you want depends on what turbulence model you use.
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