So, how does an foil air work? You can't have it many different ways. There is only one physics. It applies the same to air flow past air foils and around objects. It is known from wind tunnel tests that the air over the top surface of an air foil speeds up, resulting in a lower net pressure along the top surface than along the bottom surface. And lest you say that that is only a result of the geometry, I'd like to point out that acrobatic air planes use an air foil design that has positive camber on both surfaces. Such an air foil will have zero lift at a zero angle of attack, but will exhibit usable lift at both positive and negative angles of attack, again due to faster moving air along the 'top' surface. As I mentioned there are mathematical solutions for fluid flow around around at least two shapes, a sphere and a cylinder. In the case of a sphere the speed up is 50%, and in the cylinder it is 100% just above the surface. So, the air speeds up as it goes around trees or buildings or whatever. The lower pressure area on the back side of the object comes about due to the lower pressure (venturi effect) of the fast moving air passing by. This effect causes a 'swirling' of the air behind the object resulting in the lower pressure. You have to keep in mind that Bernoulli's Equation applies to all regions of the air flow, since no external work is done. If the air behind the object were not set in motion by the venturi effect, the pressure behind the object would be as great as the pressure in front, violating the actual physics. As far as turbulence is concerned, air flow need not be turbulent. I watched snow being blown of off a triangular shaped snow bank one time where the air slowed down and spread in an obvious laminar manner for several feet down wind of the bank. I was surprised as I expected a vortice, but that's what it did.
