CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   Main CFD Forum (http://www.cfd-online.com/Forums/main/)
-   -   Yplus (http://www.cfd-online.com/Forums/main/119630-yplus.html)

rayan24 June 20, 2013 15:37

Yplus
 
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

CONVERGE LEARNER June 21, 2013 04:22

reply of Y+
 
Hi.
Y+ represents the suitability evaluation of boundary layer thickness.

sbaffini June 21, 2013 06:50

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...

CONVERGE LEARNER June 21, 2013 07:05

another question
 
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.

sbaffini June 21, 2013 07:07

I'm sorry, but this not my field of experience.

Regards

rayan24 June 21, 2013 08:48

Verry good explanation

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

Thanks


Quote:

Originally Posted by sbaffini (Post 435257)
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...



All times are GMT -4. The time now is 02:06.