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 frossi March 10, 2017 16:02

Recirculation over wing

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Hi,

I am simulating high subsonic flow (Mach 0.75) over a wing at 2.5 deg angle of attack at ambient conditions found at 10,000 m. When I look at the velocity streamlines in my results, I get what looks like a region of very low velocity, recirculating air over the wing (see pics). How can it be? Especially given the high speed of the wing. Could it be a region of flow separation, and the low velocity is due to the turbulent flow? What's even more confusing is that such phenomenon occurs only in that specific section of the wing.

Can someone explain what could be the cause and if it is a problem for my simulation? Thank you very much.

 ghorrocks March 11, 2017 04:31

Quote:
 How can it be?
Your wing has a separation at that point. You can get separations at high Reynolds numbers and low Reynolds Numbers. If the angle of attack is high enough it will separate.

Quote:
 the low velocity is due to the turbulent flow?
This comment suggests you need to do some reading into turbulent boundary layers on airfoils. At high Re the flow over just about the entire wing will be turbulent. The recirculation will be a region of very high turbulence intensity.

Quote:
 What's even more confusing is that such phenomenon occurs only in that specific section of the wing.
It looks like it is caused by either a change of camber on the long section of wing, or a effect due to the sharp transition from one wing segment to another nearby. Both of these effects are normal design flaws which can lead to recirculations.

Quote:
 is a problem for my simulation?
You need to decide whether this effect is real or just a numerical artefact. As I have explained this effect could quite possibly be real. If you have done validation and verification of your simulation you will know whether your simulation is accurate or not. So you can work this out for yourself.

 frossi March 11, 2017 15:46

thank you, I will look into this.

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