In this project we are investigating the low frequency unsteadiness that characterizes the interaction of a shock wave with a turbulent boundary layer. This work has implications for the fatigue of structures and effectiveness of control surfaces on high speed aircraft and missiles. Our approach is to combine fast response pressure measurements with advanced optical diagnostics, such as planar laser scattering (PLS) from a condensed fog, and particle image velocimetry (PIV). An example PLS image taken in the Mach 5 wind tunnel is shown. The flow moves toward the compression ramp at the far right. The image reveals large-scale turbulent structures and their interaction with the separation shock. Sponsored by the U.S. Army Research Office.
The study of shock wave/turbulent boundary layer interactions is important in aerodynamic design due to the large fluctuating temperatures and pressures created by the unsteady motion of the separation shock. A typical interaction can be modeled in the laboratory by simplified bodies, such as the unswept compression ramp illustrated in the schematic above. The separation shock wave is displaced from the base of the ramp and moves back and forth in a random fashion. As a result of the large adverse pressure gradient across the shock, a separation bubble forms just behind it and expands and contracts in randem with the shock motion.