# Recirculation zone over airfoil in SST model

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 March 29, 2011, 07:00 Recirculation zone over airfoil in SST model #1 Senior Member   Nick Join Date: Nov 2010 Posts: 120 Rep Power: 6 Hi everyone, I've run a simulation at Re=120000 over a thick airfoil using the SST model. The solution converges and in the post I can see a re-circulation zone towards the trailing edge. I was wondering whether this is due to a turbulent boundary layer separation or laminar. Does the plain SST (no transition) mean the entire foil has undergone a turbulent boundary layer and its separation in this case? Regards, Nick

March 30, 2011, 01:53
#2
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Raashid Baig
Join Date: Mar 2010
Location: Bangalore, India
Posts: 136
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Quote:
 Originally Posted by Nick R Hi everyone, I've run a simulation at Re=120000 over a thick airfoil using the SST model. The solution converges and in the post I can see a re-circulation zone towards the trailing edge. I was wondering whether this is due to a turbulent boundary layer separation or laminar. Does the plain SST (no transition) mean the entire foil has undergone a turbulent boundary layer and its separation in this case? Regards, Nick
Hi I think you should take a look at the following forum thread, similar issue has been discussed in detail there -
Two-equation turbulent models: low re airfoils

 March 30, 2011, 19:15 #3 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,828 Rep Power: 85 If the transition model is not enabled than the turbulence model assumes the flow is turbulent everywhere. So if you see a recirc using this model then it is a "normal" separation, not a laminar separation bubble.

 March 30, 2011, 20:11 #4 Senior Member   Nick Join Date: Nov 2010 Posts: 120 Rep Power: 6 Thanks Glenn. Just to clarify. So you mean it's the turbulent boundary layer that has separated ?

 March 30, 2011, 20:15 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,828 Rep Power: 85 If you have not enabled turbulence transition model then it is using a fully turbulent model and boundary conditions everywhere. But if there is significant laminar flow about then the simulation will be inaccurate and the results rubbish.

 March 30, 2011, 20:24 #6 Senior Member   Nick Join Date: Nov 2010 Posts: 120 Rep Power: 6 I see. Thanks. Do you know of any resources that I can use to learn about cfx transition modelling? I need to learn about it as soon as possible.

 March 30, 2011, 20:27 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,828 Rep Power: 85 The references listed in the documentation are the main ones. From time to time ANSYS also runs Advanced turbulence modelling courses and these go into the transition model in detail.

 March 30, 2011, 20:43 #8 Senior Member   Nick Join Date: Nov 2010 Posts: 120 Rep Power: 6 Much appreciated.

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