Hi! I'm working on a high Reynold's number model, considering flow over an airfoil with a high angle of attack. I know I want to minimize drag. I'm told that flow separation creates pressure drag---relatively low pressure in the wake of my foil. Q1: Why would flow separation cause lower pressure downstream (relative to the pressure on the upstream surface of an object)? Sometimes flow separation causes the fluid to stagnate in the wake, or even reverse in direction. Q2: Why does flow separation cause an adverse pressure gradient and sometimes a reverse in the direction of flow? Many thanks.