Fragmentation and atomization characteristics of near-orifice liquid jet under transverse gas film

In order to understand the fragmentation and atomization characteristics of the liquid jet in transverse gasfilm, a pintle injection element using air and water as simulants is designed. The two-phase flow large eddysimulation and backlight imaging are used to study the liquid-jet breakup process and spray-field dynamiccharacteristics in the nearorifice area of pinte injection element under the atmospheric environment. Theprimary fragmentation process of the liquid jet dominated by surface wave is obtained by large eddy simulation,which reveals the establishment process of the spray field in near-orifice area of the gas-liquid pintle injector.After the subsonic airflow leaves the slit, it expands and accelerates into supersonic state. Then the decelerationand pressurization phenomenon occurs once the supersonic airflow passes through the detached bow shockupstream of the liquid jet. The liquid jet bends downstream due to the difference in pressure between upstreamand downstream, and the Rayleigh-Taylor (R-T) unstable surface wave appears on the jet windward surface. Asthe surface wave develops, the penetration of the wave trough by airflow causes the continuous liquid jet tofragment. Proper orthogonal decomposition (POD) method can effectively reconstruct spray snapshot. ThePOD mode shows that the low-frequency spray oscillation in near-orifice area is caused by the overallexpansion/contraction process of the spray field, while the high-frequency one is due to the "impact wave"movement of the liquid block or liquid mist group on the windward side. The latter is produced by the R-Tunstable surface wave before the jet breakup, and can be categorized as traveling wave structure. Thedimensionless traveling wave wavelength has a power-law relationship with Weber number