50 kHz PIV of a Swept-Ramp Shock-Wave Boundary-Layer Interaction at Mach 2.

The interaction from a 30$^{\circ}$ sweep, 22.5$^{\circ}$ compression ramp in a Mach 2 flow is examined using wide-field 5Hz and 50 kHz PIV. The high-speed PIV is fast enough to resolve the large-scale unsteady motions of the SWBLI and can be band-pass filtered to investigate the driving mechanisms of unsteadiness and the widefield PIV allows comparisons with mean flow-fields. Preliminary investigation looked at three distinct frequency bands: 10-50 kHz (0.025-0.25 $U_{\infty}/\delta_{99}$), 1-10 kHz (0.025-0.25 $U_{\infty}/\delta_{99}$), and 0-1 kHz (0-0.025 $U_{\infty}/\delta_{99}$). The unsteadiness associated with 10-50 kHz shows no correlation with the upstream boundary layer and accounts for 40% of the amplitude. The unsteadiness associated with 1-10 kHz is correlated with the upstream boundary-layer and also accounts for 40% of unsteadiness. This frequency is similar to those of boundary-layer superstructures. The unsteadiness associated with 0-1 kHz shows the strongest correlation with the upstream boundary-layer but accounts for only 20% of the amplitude. Clearly a range of unsteadiness mechanisms are present, with significant amplitude associated with higher frequencies. Future work will focus on expanding these findings with surface pressure and additional PIV.