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Old   August 28, 2008, 07:47
Default Flow Separation Behind Flap
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I am currently looking at using FLUENT with URANS and in 2D to investigate a NACA 0015 aerofoil at 0 deg angle-of-attack with a trailing-edge flap (~ 5% chord) moved from 0 to 90 degrees using a dynamically moving mesh. The mesh is very refined (~250 000 cells) particularly around the flap and I am using a very small timestep (5e-5)and the farfield ~20 chords away. When the flap is at 90 degrees (or even 30 degrees) of incidence and the flow is initialised, vortex shedding occurs and the lift coefficient on the wing is in agreement with experimental results. However, when the flap is moved from 0 degrees through to 90 degrees the flow around the flap fails to separate and appears like the flow when using RANS. Does this behaviour sound like the result of inadequate mesh refinement, too large a timestep or the turbulence model I am using?

Many thanks

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Old   August 28, 2008, 09:53
Default Re: Flow Separation Behind Flap
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Well, since you haven't told us which turbulence model you are using, it's a bit difficult to say. You also haven't told us how fast the flap is moving, or for how long you have run it after getting to 90 degrees. It is possible that the separation just hasn't had time to happen yet.

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Old   August 28, 2008, 12:19
Default Re: Flow Separation Behind Flap
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Sorry Charles. I am using the Spalart-Allmaras model and the flap moves through 90 degrees in t* = 2.5 (the time taken for 2.5 chord lengths of flow to pass). When the flow is initialised and restarted, the number of vortices shed in t* = 2.5 is roughly 10 or so). So based upon that, when the flap has moved up to 90 degrees and it has been left running for t* = 3, I would have expected vortex shedding to have started developing.


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Old   August 28, 2008, 12:54
Default Re: Flow Separation Behind Flap
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Yes, that sounds really odd. Perhaps leave it running a bit longer to see what happens.
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Old   February 2, 2010, 08:31
Default Need an help in modeling of multi element aerofoil
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I wanted to model the multi element aerofoil in gambit. Actually, I have a journal about multi element aerofoil which I need to follow to have intial knowledge. In that it was mentioned that both the wings are created with same date FX 63-137. But picture looks that main element was big and flap was small. How can he reduce the size and position of points? Could you help me in this please?
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