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Feb29-12, 10:20 AM
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boneh3ad's Avatar
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Quote Quote by tsimon View Post
Why does flow separation give less lift?

A separated "suction side" would in my pov give zero pressure (which is the lowest possible).
And low pressure on suction side is, of course, beneficial.

I think I got it now; as the pressure can not drop further a increase in angle of attack will produce less lift as the projected force (integration of pressure difference) in "lift direction" will be smaller.
First, you can't have "zero pressure" unless you are in a vacuum.

Anyway, when the flow separates, you get a separation bubble which is a local area of the flow where the boundary layer has detached and formed a circulating bubble between it and the surface. In this bubble, velocities are typically much lower than underneath. When you slow a fluid down, the static pressure rises, so now you have a higher pressure above the airfoil than below in certain points. That can lead to a loss of lift, and in some situations, even the opposite effect.