text: The basic feature of airflow separation is 
  stagnation of the lower levels of the boundary 
  ~cparation muh when the lower 
  layer. Airjh 
  lcvcls of the boundary layer do not have sujicicnt 
  kinetic cncrgy in the prwncc of an advcm ps.wrc 
  gradient. The most outstanding cases of air- 
  flow separation are shown in figure 1.26. An 
  airfoil at some high angle of attack creates a 
  pressure gradient on the upper surface too 
  severe to allow the boundary layer to adhere 
  to the surface. When the airflow does not 
  adhere to the surface near the leading edge 
  the high suction pressures are lost and stall 
  occurs. When the shock wave forms on the 
  upper surface of a wing at high subsonic speeds, 
  the 
  the increase of static pressure through 
  shock’ wave creates a very strong obstacle for 
  the shock wave is 
  the boundary layer. 
  If 
  sufhciently strong, separation will 
  follow and 
  result from the 
  “compressibility buffet” will 
  turbulent wake or separated flow. 