EXPERIMENTAL-STUDY OF FLOW SEPARATION ON AN OSCILLATING FLAP AT MACH-2.4

Measurements of unsteady wall pressures have been made in the turbulen t boundary layer just upstream of the hinge line of an oscillating fla p. The flap, which creates a highly three-dimensional compression corn er flowfield, was oscillated in fully attached, crossing incipient sep aration, and fully separated flow regimes over a range of frequencies. It was found that a substantial lag of the pressure on the flap was p roduced when oscillating across the point of incipient separation. Thi s occurred at much lower reduced frequencies than for the case of dyna mic stall on an airfoil in transonic flow. The dynamic hysteresis was much less in the fully separated case and negligible in the fully atta ched case.