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Recirculation zone over airfoil in SST model

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Old   March 29, 2011, 07:00
Default Recirculation zone over airfoil in SST model
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Nick
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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?

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Nick
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Old   March 30, 2011, 01:53
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Raashid Baig
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Quote:
Originally Posted by Nick R View Post
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
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Old   March 30, 2011, 19:15
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Glenn Horrocks
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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.
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Old   March 30, 2011, 20:11
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Thanks Glenn. Just to clarify. So you mean it's the turbulent boundary layer that has separated ?
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Old   March 30, 2011, 20:15
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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.
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Old   March 30, 2011, 20:24
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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.
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Old   March 30, 2011, 20:27
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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.
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Old   March 30, 2011, 20:43
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Much appreciated.
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