Examples of the effects of shock-induced boundary-layer separation in transonic flight

Abstract

The present state of knowledge concerning the interaction between shock waves and boundary layers, and several examples of the importance of the interaction in high-speed flight were described in a previous report. It was shown that the major effects arose from, and could be explained in terms of, separation of the boundary layer at or ahead of the shock wave. The present note gives further examples of the consequences in flight of shock-induced separation of the boundary layer; these examples have been derived from data obtained in NACA and British flight tests, and from high-speed wind tunnel experiments. The variation of the pressure coefficient at the trailing edge of the wing has been used to deduce the onset of separation from the results of the flight tests. It is found that separation occurs on straight wings at approximately the same value of the local Mach number just ahead of the shock as for two-dimensional aerofoils with turbulent boundary layers. For swept wings the available data are inadequate for a detailed comparison. Various features in the "steady-flow" characteristics and buffeting behaviour of the aircraft considered are then shown to be closely associated with boundary-layer separation. These features include wing dropping, loss of control effectiveness, and the "pitch-up" instability which has been encountered with swept-back wings.