Shock-Wave Boundary-Layer Interaction Unsteadiness Mechanisms: An Experimental Investigation using 50 kHz PIV.*

A swept shock-wave boundary-layer interaction (SWBLI) is generated from a swept compression ramp in a Mach 2 flow. The flow field is examined using 50 kHz PIV in a side view (i.e., streamwise-transverse) plane.

Previous work in the plan-view (i.e., streamwise-spanwise) plane shows that separation-line unsteadiness is associated with three Strouhal number ranges: low (St<0.01), mid (0.01<St<0.10), and high (St>0.10). Unsteadiness of each range is characteristically different from the others with its own driving mechanism(s).

Experiments in the side-view plane capture separation and reattachment and allow examination of unsteadiness of the entire separation bubble. Separation and reattachment feature broadband spectral content and are only correlated in the low-frequency band, where a ‘breathing motion’ is observed. The mid- and high-frequency unsteadiness appears uncorrelated yet possess significant unsteadiness, suggesting different mechanisms drive the separation and reattachment locations in these frequency bands. Hence, unsteadiness of a swept SWBLI appears to result from the interaction of a number of different unsteadiness mechanisms, that compete to drive the separation and reattachment locations.