# Is Y+ depends on the tubulence model?

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 September 8, 2011, 07:23 Is Y+ depends on the tubulence model? #1 New Member   Krishna Join Date: Aug 2011 Location: Japan Posts: 26 Rep Power: 8 If we use different turbulence models, the target Y+ will change accordingly?

September 8, 2011, 07:52
#2
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Raashid Baig
Join Date: Mar 2010
Location: Bangalore, India
Posts: 136
Rep Power: 9
Quote:
 Originally Posted by krishnag2002 If we use different turbulence models, the target Y+ will change accordingly?
Does you question mean -
"If you use different turbulence models we should target different Y+ while making grids ?"

 September 8, 2011, 09:18 #3 New Member   Krishna Join Date: Aug 2011 Location: Japan Posts: 26 Rep Power: 8 Yes Thanks in Advance

 September 8, 2011, 23:36 #4 Senior Member   Raashid Baig Join Date: Mar 2010 Location: Bangalore, India Posts: 136 Rep Power: 9

 September 9, 2011, 08:26 #5 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 195 Rep Power: 10 yes, it does for the turbulence model chosen, a preferable range of Y+ must be obtained to be considered valid the analysis. What drives this range will be the size of the first cell adiacent to the wall.

 September 12, 2011, 15:44 #6 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,358 Blog Entries: 6 Rep Power: 45 for example yplus 30 or greater for K epsilon based models and y+1 ~ for the SST, BSL and SA type models. It is the preferable approach. although we can extend the K epsilon model to yplus = 1 range by using the special damping functions as implemented in the Fluent similarly SST model can be used with the yplus = 30 mesh P.S: Yplus = 30 or greater implies we are not solving the viscous sub-layer (yplus 2 or less) and buffer layer (in between 2 and 30). It is also called wall function approach Yplus = 1 implies we are resolving the viscous sub layer. It is necessary to use the yplus = 1 type mesh if flow is dominated by the separation and reattachment where wall function ceases to be valid In commercial CFD codes after Yplus = 11.06 wall function approach is activated and below this viscous sub layer approach is used also check this link http://www.cfd-online.com/Forums/cfx...machinery.html

 September 13, 2011, 02:06 #7 New Member   Krishna Join Date: Aug 2011 Location: Japan Posts: 26 Rep Power: 8 thanks for your information. now I have some idea about Y+

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