The unsteady flow characteristics of water jet atomization in supersonic crossflow

This investigation examines the atomization flow characteristics and instability mechanisms in a liquid jet in supersonic crossflow (LJISC). Through concurrent deployment of high-speed imaging and phase Doppler particle analysis, we successfully captured two distinct phenomena: the spanwise vortex formation at the atomization zone's lower boundary and the periodic generation and separation of irregular droplet clusters at its apex. Our observations reveal that droplets initially present in the subsonic region were entrained into the supersonic regime by the spanwise vortex, subsequently undergoing fragmentation due to elevated frequency oscillations. To further investigate the gas–liquid interactions in shear-dominated LJISC atomization, we conducted numerical simulations using interTwoPhaseLSELCentralFoam, a compressible two-phase interfacial flow solver developed within the OpenFOAM® framework. We identified a transitional plane demarcating the subsonic-supersonic flow boundary and applied proper orthogonal decomposition (POD) to analyze the temporal evolution of velocity fields across this plane. The POD analysis revealed that shear instability-induced velocity fluctuations in the incoming flow governed the systematic formation and detachment of droplet clusters. Additionally, our findings demonstrate that spanwise-aligned counter-rotating vortex pairs facilitated droplet migration across different velocity strata.