Fast PSP measurement of three-dimensional low-frequency unsteadiness in sidewall-confined shock wave/turbulent boundary layer interaction

The presence of sidewalls exerts three-dimensional (3D) effects on shock wave/turbulent boundary layer interaction (SBLI), which results in experimental challenges due to the highly unsteady flow with complex 3D patterns. The low-frequency large-scale flow patterns of a 24 degrees sidewall-confined compression ramp interaction were investigated using fast pressure-sensitive paint. The experiment was conducted in a Mach 2.5 wind tunnel, and the unit Reynolds number was Re = 1.12 x 10(7)/m. The sampling rate of the fast pressure-sensitive paint was 4 kHz, and the spatial resolution was 0.175 mm/pixel. In-situ calibration via several pressure transducers was used to determine the time-resolved global pressure distributions. Correlation analysis and proper orthogonal decomposition analysis were used to extract the large-scale unsteady flow patterns. The time-averaged results provide a global view of the typical flow structure, which consists of primary interaction zone and corner interaction zones. The time-resolved results show the asymmetry of the instantaneous pressure distribution induced by the sidewalls, and spanwise differences of the pressure fluctuation amplitudes in the interaction zones are observed. In addition to the common streamwise breathing mode, an interesting spanwise antisymmetric mode is revealed that provides clear evidence of the strong 3D effects in sidewall-confined SBLI.