Flow Separation
Summary
Shock-Induced Separation
The interaction between a shock and a boundary layer depends on whether the boundary layer is laminar or turbulent. In the former case the pressure rise through the shock will propagate farther upstream and downstream (the shock will look weaker).
The turbulent boundary layer, though, carries more momentum and can better overcome the strong adverse pressure gradients. The figure below is a sketch of phenomena taking place when a shock is interacting with a laminar boundary layer.
Other Forms of Separation
Other forms of separation are either natural (boundary layer, leading edge), controlled (fences, tip devices) or enhanced (strakes, vortex generators). Of particular interest is the separation enhanced by strakes or other leading edge extensions (smooth wing attachment), that is used to improve the aircraft transonic manouevrability at high angle of attack.