Internal aerodynamics of supersonic crossflows with transverse liquid injection

This study experimentally investigates the internal aerodynamics of transverse liquid injection in a supersonic crossflow (Mach 2.1) using two configurations: single and tandem (8 mm spacing) at three injection mass flow rates. Back-lit imaging revealed classical jet breakup phenomena, including surface wave instabilities with increasing amplitudes along the jet boundary, leading to protrusions, breakup into large liquid clumps, and their disintegration into finer droplets under aerodynamic forces. The single injection exhibited large liquid clumps forming further downstream than the tandem injection. Schlieren imaging showed that at a low momentum flux ratio ( J = 0.94 ), both configurations produced regular reflection (RR) of the bow shock wave from the top wall. Increasing J to 1.90 resulted in RR for the single injection, while the tandem injection transitioned to Mach reflection (MR). At J = 2.67 , both configurations exhibited MR. The earlier RR-to-MR transition in tandem injection is attributed to its higher jet penetration and spanwise spread, reducing the downstream crossflow passage area, acting as a supersonic diffuser, and increasing downstream pressure, which is favorable for MR transition. It was also observed that the bow shock wave oscillations strongly depend on the surface oscillations of the liquid jet, with both oscillation frequencies closely matching. Separation zones were observed at the bottom wall due to bow shock wave-boundary layer interaction and at the side walls due to the Mach stem of the MR structure interacting with the walls. These interactions create complex flow regions dominated by vortex structures, significantly influencing the overall flow dynamics. © 2025 Author(s).