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[Other] How to estimate y+ and set cell division for K-epsilon turbulence model in openFOAM?

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Old   December 23, 2014, 22:29
Exclamation How to estimate y+ and set cell division for K-epsilon turbulence model in openFOAM?
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Mominul MuKuT
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Good morning all!
As I told earlier about my simulation in a wind tunnel. I am expecting separation in the diffuser region, to get expected separation proper cell division is necessary. For standard k-e turbulence model I learned from the previous replies that it better to use y+>30. I have found these two sites to calculate y+
http://www.pointwise.com/yplus/
http://www.cfd-online.com/Tools/yplus.php
Here is my simulation domain:


Straight section height is 200mm which is 630mm long and a diffuser section with 20deg inclination having a length of 250mm.
In the above two y+ calculation site, there is a term boundary layer length and reference length, I am confused with these two term because both sites calculates the same but they mention these terms differently. Shall I use this length as 200mm? But in diffuser section these vertical height is a varying height, as it has 20deg slope in bottom wall.
BR
MuKuT
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Old   December 31, 2014, 16:58
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Using adimensional parameters is just a way of having a first idea of the magnitude of magnitudes such as yplus. Use the total length of your domain and once you run the simulation use the tool named yPlus in openfoam to know exactly the value of yplus
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Old   February 4, 2015, 04:37
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Mominul MuKuT
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Quote:
Originally Posted by ssss View Post
Using adimensional parameters is just a way of having a first idea of the magnitude of magnitudes such as yplus. Use the total length of your domain and once you run the simulation use the tool named yPlus in openfoam to know exactly the value of yplus
Thanks a lot. I am using k-omega-SST model instead of K-E now to get more realistic separation as it was found during experiment. In preliminary stage new simulation gives better result than K-E model.
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