Experimental investigation on flow characteristics and instability of submerged high-speed gaseous jets under co-flow

Submerged high-speed gaseous jets exhibit complex evolution and instability mechanisms due to the significant density and velocity differences between the gas and the surrounding water. This study experimentally investigates the high-speed gas jet generated by a Laval nozzle positioned behind a rotating body under various co-flow velocities. Based on the Eulerian approach to fluid dynamics, width-time maps visualizing jet width changes at specific cross-sections were generated. Utilizing high-speed shadowgraph images, pressure sensor data and the width-time maps, this study examines the evolution characteristics of jet and the pressure oscillation characteristics behind the rotating body, categorizing the jet evolution into three basic stages. This research also investigates the correlation between back pressure oscillations and jet morphology, noting that peaks in local back pressure correspond to the jet's core area being blocked. A specially developed interface tracking algorithm is used to extract the normal acceleration of the jet interface, facilitating an analysis of the impact of Kelvin-Helmholtz and Rayleigh-Taylor instabilities on jet the instability of the jet interface. •A novel approach is employed to characterize the spatiotemporal evolution of the jet width at specific axial sections.•The investigations indicate the local back pressure peaks correspond to the jet's core area being blocked.•The respective influences of R-T and K–H instability mechanisms are calculated by the developed algorithms.