Unsteadiness characterization of shock wave/turbulent boundary layer interaction controlled by high-frequency arc plasma energy deposition

We carried out an experimental study of Mach 2.5 airflow over a semicircular column with 15 kHz arc plasma energy deposition (APED). The APED was pulsed at microsecond time scales, and it rapidly added high-repetition-frequency thermal bubbles that propagated downstream. Time-resolved schlieren imaging with a frame rate of 30 kHz was utilized to record the dynamic flow fields. This study was aimed at investigating the effects of these thermal bubbles on the unsteadiness characterization of a shock wave/turbulent boundary layer interaction (STBLI) by some statistical methods based on the spatial gray value extracted from a sequence of time-resolved schlieren images. The results showed that APED pulsed at 15 kHz was highly effective in weakening both the separation shock and the attached shock continuously and in narrowing the low frequency component of the oscillatory separation shock. A stronger oscillation of the attached shock under APED was found. The thermal bubbles increased the characteristic scales of vortex in the incoming turbulent boundary layer and shear layer, enhancing the fluctuation of the shear layer with large numbers of high-frequency components. The continuous transforming of the enlarged eddies along the shear layer was regarded as the main cause of shock weakening and frequency modulation of the STBLI in this study.