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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)?

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Separated turbulent flow is typically at lower pressure than surrounding air, it is a cause of "pressure drag".

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  • $\begingroup$ It seems such area has relatively lower velocity, so can you explain why it dose not have higher pressure? Also can you explain why aurfoil lift reduce after separation? $\endgroup$ – S.Serpooshan Sep 1 '17 at 16:07
  • $\begingroup$ 1) speed and density are independent variables $\endgroup$ – JMLCarter Sep 1 '17 at 23:31
  • $\begingroup$ 2) due to drag slowing the whole aerofoil $\endgroup$ – JMLCarter Sep 1 '17 at 23:32
  • $\begingroup$ 1) speed and density(?) or pressure you mean? what about bernoulli equation. 2) but wind tunnel experiments with constant air speed shows lift reduce after separation (even when speed is kept constant) $\endgroup$ – S.Serpooshan Sep 2 '17 at 5:08
  • $\begingroup$ 1) speed and density $\endgroup$ – JMLCarter Sep 2 '17 at 21:11

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