Low-frequency unsteadiness of shock-wave/boundary-layer interaction in an isolator with background waves

Low-frequency unsteadiness is investigated through wind tunnel experiments and numerical simulations of the internal flow in a supersonic isolator with background waves generated by a 14 degrees wedge in a freestream with a Mach number of 2.94. The power spectra, coherence, and phase analyses of high-frequency pressure signals and schlieren images provide a local and global description of the unsteadiness. The upstream mechanism exhibits a significant influence on the unthrottled flow field. In the weak interactions of small separation flow, the pressure fluctuation between two adjacent incident points has a strong correlation in a large frequency range, while only large-amplitude shock oscillations are exhibited in the pressure fluctuations at the boundary layer. The downstream mechanism dominates the asymmetric shock motion in the throttled flow field. The profiles of the power spectrum and standard deviation both exhibit two peaks at the upstream and downstream peripheries of the wall separation patterns. Two types of oscillations can be identified through the pressure data, and type III is established from the analysis of schlieren images. The oscillation behavior of the three types is obtained through the power spectral analysis of a series of schlieren snapshots. The frequency of the occurrence and the one-cycle amplitude of different oscillation types are significantly different. By combining the coherence and phase analyses with the corresponding schlieren images and pressure data, the feedback mechanism of the three oscillation types is determined. This study combines the low-frequency unsteadiness in supersonic internal flows with the multiple separation regions caused by complex background waves.