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In the 3D case,downward turning is immediately above and below the wing is stronger than in 2D case,for the same lift.This is because more rapid dying off the pressure above and below the airfoil means the vertical pressure gradient near the wing surface is stronger than in 2D case.The airfoil pressure field dies out more rapidly ahead of the airfoil and behind,which results in less upward turning of the flow in this region.So in 3D case we have more downward turning above and below the wing and less upward turning ahead and behind.Vertical extent of pressure distribution in 3D is lower than in 2D for the same chord and lift per unit span. Reducing vertical extent of pressure distribution means increase pressure gradient close to the wing surface and a reduction far from the surface.

So in short, smaller vertical extent(small pressure field) of pressure=larger pressure gradient=larger force which drives downward accelaration.

Pressure gradient=delta pressure / distance (Pa/m)

Do you see some contradictory in explanation above or everything is logically?

because,when we increase AoA,vertical extent of pressure distribution is larger so pressure gradient is smaller and downward acceleration must be also smaller,but it isnt because with AoA rise downward turning(downwash) as well.

Can someone explain in detail what happend with pressure fields,pressure gradient in relation to upwash/downwash at 2D/3D wing and when change AoA...

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  • $\begingroup$ I think this is a great question or at least a nice way of looking at things. had to read it a couple of times to understand what you were asking. I don't have a good overall answer, unfortunately, preferably an intuitively grabbable one at the moment. Hopefully, someone else here might be able to shed some light on this. Ideally, I think one can tackle this by justifying the use of 2D horseshoe vortex sheet instead of 3D doublet sheet when modeling the wing. $\endgroup$
    – user46017
    May 6, 2020 at 1:58

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Take a look at https://www.sciencedirect.com/topics/engineering/angle-of-attack and https://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/lift_formula.html. Lift graphs have a linear portion for small angle of attacks (and in 2D scenarios), but drag and airflow (laminar (non-shedding) vs. turbulent (shedding)) are both are non-linear, and both affect pressure and thus lift, and are important in real-life and 3D calculations.

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    $\begingroup$ Links have a tendency to break over time. Would you mind editing a few of the important parts of those pages into your answer? $\endgroup$
    – dalearn
    May 3, 2020 at 20:45

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