Is Turbulence Necessary for Lift on a Wing?

[russ_watters]

@russ_watters, regarding post #48, I've tried to infer your way of viewing lift. Am I correct in my description of your thoughts below?
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Yes, that's basically what I'm saying. Also, I really dislike the flat plate since the airflow over the top surface is just such a mess. But at least in that pic you can see the stagnation point down under the "chin" and the airflow curving up to meet the airfoil before it even gets to it.

 

[Arjan82]

Just to be clear, I look at this now strictly from an earth-fixed reference frame, so the foil is moving and the box is standing still.

I'm not sure if you mean that literally. A point by definition has zero size. While I guess it is possible that a single molecule is sitting on the leading edge, straddling the stagnation point, I doubt it. Air certainly doesn't pile-up there.

That there is a forward velocity component doesn't mean the air piles-up. Take an air parcel as close to the stagnation point as you can. At this stagnation point a tangent line to the foil is vertical. What you suggest is that if the foil starts moving this air parcel never moves forward but just directly upward (or downward). I find that unlikely since the wall can only push in horizontal direction (ignoring friction) or, because a parcel has a finite size and the tangent point is indeed a point, the wall will move the parcel nearly only forward. Because of continuity the other parcels around it also need to have a forward velocity component albeit somewhat lower.

If air molecules get slowed down as they approach the stagnation point, they must be accompanied by air molecules further away (vertically) that speed up, so the average velocity is higher.

So, following the frame of reference of the foil the approaching air 'slows down' as you say. But from the frame of reference of the box, the air was already not moving. Thus the approaching foil 'speeds up' the air in the other direction, forward that is :).