Flowfield Measurements in a Mach 2 Fin-Generated Shock/Boundary-Layer Interaction

Abstract

An experimental study is conducted on the interaction of a swept shock wave with a turbulent boundary layer. The shock wave is generated by a sharp unswept fin in a Mach 2 flow, where the strength of the interaction is varied from weak to moderate by changing the angle of attack of the fin from 10 to 15 deg, which corresponds to a normal Mach number of 1.3 and 1.4, respectively. Surface oil-flow visualization is used to study the topography of the interaction where surface flow features such as the upstream influence line and the separation lines are identified. By taking advantage of the quasi-conical symmetry of the flowfield, velocity field measurements are acquired in the conical reference frame for the interaction at the moderate interaction strength of at two locations from the fin apex. Flowfield features such as the -shock structure, slip line, and the separation bubble with the reverse flow are clearly visible in the velocity field. These results are also examined in the spherical coordinate frame, and good agreement in the spatial location of the critical features is found, providing direct quantitative, experimental evidence of quasi-conical symmetry of the flowfield above the surface. An examination of the velocity field downstream of the rear-foot of the -shock shows a region (a “streamtube,” bounded on one side by the slip line emanating from the triple point) where the flow accelerates to transonic and supersonic speeds. This flow eventually turns toward and impinges upon the flat plate, a phenomenon referred to as an “impinging jet” in the literature. It is believed to be the principal cause of the high mean, unsteady pressures, very high heating, and skin friction coefficients that the present measurements confirm. An examination of the turbulence kinetic energy reveals a significant increase in amplitude in the separated flow region that is bounded by the flattened vortex under the -shock.