Accuracy of Boundary Layers With Turbulence Models

de5truction · May 6, 2011, 05:42

Hi,

I am quite confused with the accuracy of boundary layers with turbulence models. For flows over a typical wing, there will be a laminar BL, transition region and turbulence BL in theory. but what I have read and understood is that turbulence models do not allow for that laminar BL and transition region (at least in Fluent) so boundary layer will be 'turbulent' throughout.

so how do CFD computations relate with reality? are they truly comparable in that sense? or is there something lacking in my understanding.

Thank you in advance.

de5truction · May 7, 2011, 11:13

Hope someone out there can help me with this urgent qn!

skullCFD · June 3, 2011, 19:36

k-e with Enhanced Wall Treatment will care of it. If Re is in low transition region, a viscous/laminar correction to the RANS can be applied (SST). But still, RANS models fail to very accurately predict the flow field for many cases especially in the transition region. I believe LES is a slightly better option (if you have a very performance machine) but even that neglects eddies smaller than Kolmogorov eddies.

May 6, 2011, 05:42	Accuracy of Boundary Layers With Turbulence Models	#1
de5truction New Member yong Join Date: May 2011 Posts: 2 Rep Power: 0	Hi, I am quite confused with the accuracy of boundary layers with turbulence models. For flows over a typical wing, there will be a laminar BL, transition region and turbulence BL in theory. but what I have read and understood is that turbulence models do not allow for that laminar BL and transition region (at least in Fluent) so boundary layer will be 'turbulent' throughout. so how do CFD computations relate with reality? are they truly comparable in that sense? or is there something lacking in my understanding. Thank you in advance.

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May 7, 2011, 11:13		#2
de5truction New Member yong Join Date: May 2011 Posts: 2 Rep Power: 0	Hope someone out there can help me with this urgent qn!

June 3, 2011, 19:36		#3
skullCFD Member Join Date: Apr 2011 Posts: 30 Rep Power: 15	k-e with Enhanced Wall Treatment will care of it. If Re is in low transition region, a viscous/laminar correction to the RANS can be applied (SST). But still, RANS models fail to very accurately predict the flow field for many cases especially in the transition region. I believe LES is a slightly better option (if you have a very performance machine) but even that neglects eddies smaller than Kolmogorov eddies.