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Shock drag

Shock drag

  • The sudden extra drag which is such a marked feature of the shock stall has two main components. First, the energy dissipated in the shock wave itself is reflected in additional drag (wave drag) on the aerofoil. 
  • Secondly, as we have seen, the shock wave may be accompanied by separation, or at any rate a thickening of and increase in turbulence level in the boundary layer. Either of these will modify both the pressure on the surface and the skin friction behind the shock wave.
  • So this shock drag may be considered as being made up of two parts, i.e. the wave-making resistance, or wave drag, and the drag caused by the thick turbulent boundary layer or region of separation which we will call boundary layer drag.
  • As has already been explained the shock wave and the thickened turbulent boundary layer or separation are like the chicken and the egg – we don’t know which comes first; what we do know is that when one comes so does the other.
  • That is not to say that they are by any means the same thing, or that they have the same effects, or that a device which reduces one will necessarily reduce the other.

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