Is Y+ depends on the tubulence model?

krishnag2002 · September 8, 2011, 08:23

If we use different turbulence models, the target Y+ will change accordingly?

cfd_newbie · September 8, 2011, 08:52

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 ?"

krishnag2002 · September 8, 2011, 10:18

Yes Thanks in Advance

cfd_newbie · September 9, 2011, 00:36

These 3 links might be useful -
http://www.cfd-online.com/Forums/mai...ga-models.html
http://www.cfd-online.com/Wiki/RANS-...bulence_models
http://www.kxcad.net/STAR-CCM/online...ulence-15.html

mettler · September 9, 2011, 09:26

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.

Far · September 12, 2011, 16:44

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

krishnag2002 · September 13, 2011, 03:06

thanks for your information. now I have some idea about Y+

September 8, 2011, 08:23	Is Y+ depends on the tubulence model?	#1
krishnag2002 New Member Krishna Join Date: Aug 2011 Location: Japan Posts: 26 Rep Power: 15	If we use different turbulence models, the target Y+ will change accordingly?

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September 8, 2011, 10:18		#3
krishnag2002 New Member Krishna Join Date: Aug 2011 Location: Japan Posts: 26 Rep Power: 15	Yes Thanks in Advance

September 9, 2011, 00:36		#4
cfd_newbie Senior Member Raashid Baig Join Date: Mar 2010 Location: Bangalore, India Posts: 135 Rep Power: 16	These 3 links might be useful - http://www.cfd-online.com/Forums/mai...ga-models.html http://www.cfd-online.com/Wiki/RANS-...bulence_models http://www.kxcad.net/STAR-CCM/online...ulence-15.html

September 9, 2011, 09:26		#5
mettler Senior Member Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 211 Rep Power: 18	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, 16:44		#6
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	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, 03:06		#7
krishnag2002 New Member Krishna Join Date: Aug 2011 Location: Japan Posts: 26 Rep Power: 15	thanks for your information. now I have some idea about Y+