Review Note

Explain the separation of a BL behind a cylinder (or other blunt body)

In frictionless flow external, fluid is accelerated from D to E, and decelerated from E to F; corresponding to pressure decrease then increase
Following the streamlines, the external flow velocity being frictionless and being under the influence of a pressure field arrives at F with the same velocity it had at D
But inside the boundary layer, we still have the same pressure field because the external pressure is impressed on the boundary layer, but now frictional forces are important
The frictional forces consume a large amount of the kinetic energy from D to E so that the remainder is unable to take the particles from the E to F
The particles therefore can't make it to F, it's motion stops, and external pressure causes it to move in the opposite direction which eventually leads to separation