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What specifically happens to air flowing over a wing?

I am wondering what happens to air over a wing, for some odd reason I can't figure it out because everything else I look up says otherwise.

I know air flowing over a lifting wing accelerates due to the slope created by AOA, and thus causes the air pressure to lower. But my question is, does the air temperature over a wing change, does the air expand or compress. I know the air compresses at the leading edge, but air must expand when its pressure is forced to lower right?

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74952ed678a6 profile image
tqo0t0jxaa profile image

"does the air temperature over a wing change"

To some extent, yes, but I'm not able to find any equations that govern the amount for non-ideal gases.

"does the air expand or compress."

Yes. As the wing encounters the air, compression and expansion occur. Air is a very compressible fluid.


qyasj5w1aa profile image

AOA is the geometric angle between the relative wind vector and the chord of the wing.

Yes, aerodynamic lift is the result of a pressure differential between the upper and lower surfaces of the airfoil. When the air flows over the upper camber, it compresses, the pressure is lower and due to the continuity equation (since air is treated as a fluid in every sense) the velocity increases. I guess you can say there are two forms of lift, pressure lift which is more dominant at low AOA, and then reaction lift, which is more dominant at very high AOA.

When the air flows over the top, yes it compresses, and due to the compression, the temperature drops. This is why on days when the relative humidity is high, when airplane takes off, during its rotation phase is you typically will see condensation form at or just aft of the wing's LE, which is where the center of pressure is usually located, that's considered the "strong point" of the wing's lift distribution from the profile aspect. As the air flows past the wing and beyond it, there is pressure recovery, and since there is no more interference from a moving body the air returns to rest (assuming a stationary atmosphere for simplicity) as it it were before it was disturbed by the wing.

Note: There are more advanced theories of lift but I am keeping this as basic and rudimentary as possible.