Mitek,

These are pictures showing the pressure distrubution around the foil. The green is lower pressure the red is higher pressure. When a boundary layer seperates it causes the pressure difference between the lower and the up surface to equalize...just like a cylinder that is not spinning...so the lift is reduced. No pressure differance NO LIFT. The higher the pressure difference the greater the lift. At the leading edge of the foil there is a stagnation area were the air doesn't know wether to go above the wing or below so it kind stops and spins....this is frontal area drag or a type of parasitic drag. One set of pictures is showing the flow of air the other is showing the pressure that is being created because of air flow. Kind of like looking at the two sides of a coin. The way the air flows over a wing is only important because it creates pressure differences. Without the pressure differences there is no lift no matter what the shape.

Steve