Not stall

thais_b · December 27, 2010, 15:05

Hi!
I searched in the entire forum and did not find a precisely answer so i am posting my problem (I'm new in CFX).
I'm working with 2D simulation of NACA 0012, with a mesh (unstructured) designed in ICEM. My Cl values seems very good until the stall angle.
The cl gets higher and higher while the AOA attack increases. I can see in the post that the separation occured with a streamline, but the cl remains increasing.
I used the SST isothermic model.

Thanks!

ghorrocks · December 28, 2010, 04:05

Getting accurate models after stall is difficult. You probably won't be able to do it using SST, you will probably need a very careful validated LES/SAS/DES model.

thais_b · December 28, 2010, 18:56

Thanks for your answer!
But, what you mean with careful validated ?
I tried to use these models and the cl values get close but they remain higher. Do you think it can be related only to my mesh quality? I checked in ICEM and the transition near the airfoil wasn't abrupt, and the quality was good.

Thanks again.

ghorrocks · December 29, 2010, 05:44

Validated means you have ensured the mesh, convergence, time step and other numerical parameters are correctly set to give the required level of accuracy.

The LES/SAS/DES models will require different time steps and meshes to the RANS models.

December 27, 2010, 15:05	Not stall	#1
thais_b New Member Join Date: Dec 2010 Posts: 10 Rep Power: 15	Hi! I searched in the entire forum and did not find a precisely answer so i am posting my problem (I'm new in CFX). I'm working with 2D simulation of NACA 0012, with a mesh (unstructured) designed in ICEM. My Cl values seems very good until the stall angle. The cl gets higher and higher while the AOA attack increases. I can see in the post that the separation occured with a streamline, but the cl remains increasing. I used the SST isothermic model. Thanks!

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December 28, 2010, 04:05		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Getting accurate models after stall is difficult. You probably won't be able to do it using SST, you will probably need a very careful validated LES/SAS/DES model.

December 28, 2010, 18:56		#3
thais_b New Member Join Date: Dec 2010 Posts: 10 Rep Power: 15	Thanks for your answer! But, what you mean with careful validated ? I tried to use these models and the cl values get close but they remain higher. Do you think it can be related only to my mesh quality? I checked in ICEM and the transition near the airfoil wasn't abrupt, and the quality was good. Thanks again.

December 29, 2010, 05:44		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Validated means you have ensured the mesh, convergence, time step and other numerical parameters are correctly set to give the required level of accuracy. The LES/SAS/DES models will require different time steps and meshes to the RANS models.