Abstract
The evolution of interfaces for underwater gas jets is the main morphological manifestation of two-phase unstable interaction. The high-speed transient photographic recording and image post-processing methods are used to obtain the interfacial change in a submerged gaseous jet at different stages after its ejection from the Laval nozzle exit. The relationship between the pressure pulsation in the wake flow field and the interfacial change is further analyzed by combining the experimental results with computational results. A theoretical model is employed to address the competition dominant mechanism of interface instability. The results show that the jet interface of a supersonic gas jet gradually changes from one containing wave structures to a transition structure, and finally forms a steady-state conical jet. The fluctuation of the jet interface results in the pulsation of the back-pressure. The dominant mechanism of the interface changes with the development and distribution of the jet, from Kelvin-Helmholtz (K-H) instability beyond the nozzle exit changing to Rayleigh-Taylor (R-T) instability in the downstream.
Highlights
Underwater supersonic gas jets are widely used in underwater propulsion, the chemical industry, and metallurgy [1,2,3]
After the high-speed gas is ejected from the nozzle, the gas flow will be blocked by water, and flow field parameters will decay rapidly, resulting in complex phenomena such as interfacial changes and vortex motion [4]
In the initial period of injecting of underwater supersonic gaseous jets, the gas flow is established with the blocking effect of water
Summary
Underwater supersonic gas jets are widely used in underwater propulsion, the chemical industry, and metallurgy [1,2,3]. In an aqueous medium environment, the flow field structures formed by high-speed jetting differ from those in air. As the density of water is more than 800 times that of air, the inertia of water shows a greater effect. After the high-speed gas is ejected from the nozzle, the gas flow will be blocked by water, and flow field parameters will decay rapidly, resulting in complex phenomena such as interfacial changes and vortex motion [4]. The evolution of the gas-liquid boundary and interface instability are the main morphological manifestations of two-phase interaction. Research into its changing characteristics is important to understand the shock-wave-induced pressure oscillation in the wake region of underwater supersonic jets
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