Unsteady Motion in the Supersonic Flow over a Wall-Mounted Hemisphere

Abstract

Experiments were performed within Rutgers University’s Mach 3.4 wind tunnel to visualize the unsteady flow over a wall-mounted hemisphere using high-speed schlieren imaging and stereoscopic particle image velocimetry (SPIV). The hemisphere () was placed within the wind tunnel’s naturally developing turbulent boundary layer, resulting in a boundary-layer thickness-to-radius ratio of 0.43. The hemisphere flowfield demonstrates many features that are characteristic of a traditional shock/boundary-layer interaction, such as unsteady motion associated with the foot of the upstream separation shock and subsequent incipient separation. In addition, a strong reattachment shock emanates from the forward side of the hemisphere where flow reattachment occurs. Cross correlation of the high-speed schlieren data indicates that the upstream shock-dominated flow is not strongly correlated with the downstream wake flow. The upstream shock structure dominates; it wraps around the sides of the hemisphere, leading to a potentially far-reaching influence. The SPIV velocity fields reveal the presence of a highly unsteady wake structure with a separated shear layer and a downstream recompression shock. The observations are consistent with recent studies concluding that the wake flow comprises two recirculating lobes with symmetry along the spanwise centerline. Turbulence statistics of the hemisphere wake and separated shear layer were also analyzed.