50 kHz PIV Investigation of Swept Compression Ramp Shock / Boundary Layer Interactions

The shock/boundary-layer interaction (SBLI) of a swept (30$^{\circ}$) compression ramp (22.5$^{\circ}$) in a Mach 2 flow is examined using 5 Hz and 50 kHz PIV in both streamwise-tranverse and streamwise-spanwise planes. The mean u-velocity component exhibits conical symmetry in accord with previous studies, but the weaker velocity components (v, w) do not. We argue that moderately-swept interactions possess an extended inception region where the separated flow takes additional distance to reach its asymptotic state. The high-speed PIV is band-pass filtered to investigate driving mechanisms of unsteadiness of the separated flow. We looked at three distinct frequency bands: low (0-1 kHz), mid (1-10 kHz), and high (10-50 kHz). Unlike unswept interactions, the majority (80%) of the amplitude exists in the mid- and high-frequency bands. The mid-frequency unsteadiness appears correlated with inflowing velocity fluctuations that are most likely driven by boundary-layer superstructures. The high-frequency unsteadiness seems related to shear layer activity and a new high-frequency mechanism related to structures in the separated flow. The unsteadiness of this swept-ramp SBLI is then compared to a similar unswept compression ramp to show differences between 2D and 3D interactions.