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April 30, 2012, 14:05 
NACA 0012 Komega model

#1 
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Join Date: Jun 2011
Posts: 48
Rep Power: 6 
Hello everyone,
I'm struggling to get a komega model to run a FLUENT simulation of a naca 0012. The 0012 is at zero degrees angle of attack, with a chord of 1 meter. The rectangular domain is a tet mesh whose inlet is 20 meters upstream and outlet is 40 meters downstream with the top and bottom of the domain at +/ 20 meters from the airfoil. It should be a big enough domain and a fairly simple and classic simulation. This sounds like a very broad question but how would I get the kw model to produce good results? My understanding is that kw has the potential to predict transition so could kw run at a Re# of say 1.3 million by specifying the inlet velocity of 20 m/s? It doesn't seem to work when I tried it. The velocity contours show a low velocity bubble around the airfoil and then acceleration way downstream. kw can also do compressibility apparently. So I tried running a density solver with the energy equation on, and the kw compressibility option turned on. I used pressurefarfield conditions for the inlet, top and bottom of the domain (M=0.8) and a pressure outlet with a turbulent intensity of 0.1%. That solution diverged. Sooooo it should be a fairly simple simulation. I'm not sure what I'm doing wrong here. I was able to get a kepsilon model to run assuming a turbulent Re# (about 4.8 million; inlet velocity 70 m/s). If I step outside of this regime,I would have to change models because my flow would not be fully turbulent, which is my whole motivation for trying to get a kw model to run at both low Re# and compressible flows. One issue might be the turbulent intensity and viscosity ratio. I set 0.1% for the intensity because I read on cfdonline that's an estimate for intensity for external flows around aircraft/cars/etc. could be much less than 1%. I left the viscosity ratio as 10 and it worked out very well for the ke turbulent case that I ran. Any ideas of how to get some meaningful results? Thanks! 

May 1, 2012, 14:41 

#2  
Senior Member
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 675
Rep Power: 13 
Quote:
It can, but that doesn't mean it's recommended. If you want best results with any CFD modelling, stick with incompressible pressure based solver unless it's required. whenever the density based solver w/ energy equation is used there is always the chance for the flow to diverge rapidly from having the wrong initialization. Your initialization has to be good, probably with a converged pressurebased solver solution. 

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