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Old   June 20, 2013, 15:37
Default Yplus
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rayan
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Hi,

I want to know what's the "Y+" and what's the effect of YPLUS, WHY i MUST CHOISE az define value for Yplus,

in LES model why i must choise Yplus =1?

Thanks for your explications
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Old   June 21, 2013, 04:22
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Hi.
Y+ represents the suitability evaluation of boundary layer thickness.
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Old   June 21, 2013, 06:50
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Y+ is importsant in relation to the known features of turbulent velocity profiles near the wall. For Equilibrium boundary layers, at low y+ (<5) it is linear, for high values (>30-50) and up to 0.1 delta (thickness of the boundary layer) it is logarithmic. For the first point near the wall in your grid you can define a value for y+, then you know if it is too high to resolve the full velocity profile or not. If not, you need a low Re turbulence model (which can go down to the wall), otherwise you will need a standard model with wall functions.

This is the basic matter in RANS.

For LES it is quite different and y+ alone is useless. Wall parallel grid spacings matters as well. But this is a much longer story...
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Old   June 21, 2013, 07:05
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That is a wonderful explanation.
Well,may I know if you know about the Detailed chemical reaction mechanism of gasoline and suitable references on this matter? Any help would be greatly appreciated.
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Old   June 21, 2013, 07:07
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I'm sorry, but this not my field of experience.

Regards
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Old   June 21, 2013, 08:48
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Verry good explanation

Thanks a lot I begin to undestund the importance of Y+

Thanks


Quote:
Originally Posted by sbaffini View Post
Y+ is importsant in relation to the known features of turbulent velocity profiles near the wall. For Equilibrium boundary layers, at low y+ (<5) it is linear, for high values (>30-50) and up to 0.1 delta (thickness of the boundary layer) it is logarithmic. For the first point near the wall in your grid you can define a value for y+, then you know if it is too high to resolve the full velocity profile or not. If not, you need a low Re turbulence model (which can go down to the wall), otherwise you will need a standard model with wall functions.

This is the basic matter in RANS.

For LES it is quite different and y+ alone is useless. Wall parallel grid spacings matters as well. But this is a much longer story...
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