I heard sometimes that the pressure inside separated flow wakes are relatively low. For example, if we place a plate perpendicular to the fluid flow, we have large vortex and wakes behind the plate. The pressure behind the object is usually considered low (like as a suction) while its front pressure is high. This gives a large pressure difference between the front and back sides of the object and so produce a drag (pressure drag).
So, is there any general rule about the fluid pressure inside the wakes when we have separation (in comparison with attached flow or less wake area)? If yes, could you explain why?
as another sample, if we consider an airfoil inside a flow, how does separation affect the pressure inside the circular wake flows. Is it higher or lower than when we have no separation (in similar conditions)?