Unsteady separation region characteristics within a normal shock wave–lambda foot structure

Within the present shock-wave–boundary-layer interaction study, the unsteady behavior of the flow separation zone within a normal shock wave and the associated lambda foot structure are considered. Also provided are correlation and time-lag data for this separation zone length relative to the normal shock wave, as well as relative to other phenomena at other flow locations. Employed for the study is a test section with an inlet Mach number of 1.54, where shock waves are visualized with a shadowgraph visualization arrangement, along with simultaneous acquisition of time-resolved surface static pressure data. Resulting instantaneous separation zone length variations are then compared to other flow phenomena and sensor data using magnitude-squared coherence and time-lag analysis. Considered are both high and low inlet Mach wave intensity distributions at the test section entrance, denoted HMWI and LMWI. Overall data trends indicate that separation length flow events at different frequencies are generally more strongly correlated with unsteady surface static pressure and with the instantaneous tracked normal shock-wave location with HMWI, relative to the LMWI arrangement. With HMWI, results for the lowest frequencies considered indicate that unsteady flow events propagate from the separation zone to the normal shock-wave location, and then to the Kulite surface location beneath the flow separation zone. In contrast, with LMWI, results for the lowest frequencies indicate that unsteady flow events propagate from the normal shock-wave location to the Kulite surface location beneath the flow separation zone, and then, to the separation zone.