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-   -   How to decide Y plus (https://www.cfd-online.com/Forums/main/105851-how-decide-y-plus.html)

 prashant810 August 10, 2012 13:23

How to decide Y plus

Hello All,

I have question how to decide the y plus?

 pete August 10, 2012 13:50

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

 prashant810 August 12, 2012 02:52

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.

 pete August 12, 2012 03:29

What y plus you want depends on what turbulence model you use.

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