Experimental Study into the Effects of Forced Transition on a Shock-Wave/Boundary-Layer Interaction

This study investigates the effects of boundary-layer tripping on an oblique shock-wave reflection (M = 1.7, Re-infinity = 35 x 10(6) m(-1)) by means of particle image velocimetry. Laminar boundary layers are sensitive to adverse pressure gradients, and the interaction with an oblique shock wave (theta = 3 deg) results in the formation of a large separation bubble (similar to 45 delta(95)). The bubble can be removed by tripping the boundary layer a short distance upstream of the incident shock wave. Three types of tripping devices were investigated in this study: a stepwise trip, a patch of distributed roughness, and a zigzag strip. The step was found to be least effective at tripping the boundary layer, yielding a turbulent boundary layer similar to 55 delta(95) downstream of the trip; whereas the other two trips required a distance of only similar to 30 delta(95). Consequently, at the same trip-to-shock-wave distance, the step was found to be less effective at removing separation than the other two trips. Although tripping the boundary layer allows for the removal of the separation bubble, it does come at the price of having a substantially thicker boundary layer (similar to 50%) downstream of the interaction.