Swirl injectors play a pivotal role in the combustion components of liquid rocket engines, underscoring the paramount importance of accurate atomization modeling. In this study, we use a coupled Eulerian-Lagrangian approach to conduct high-precision simulations of fully developed atomization. These simulations are rigorously compared with experimental atomization patterns observed under cold conditions and during ignition phases. The results exhibit a remarkable consistency in atomization patterns and the spatiotemporal evolution of droplet morphology. The simulations yield high-resolution three-dimensional atomization images, capturing intricate perturbation wave structures whose evolution periods closely align with experimental findings. The resultant vortex structure field vividly depicts the evolution of these perturbation waves from the injector's interior to its exterior. The periodic intervals of unstable waves are governed by the impact of the upward gas swirl on the edge line of the injector's straight section. Furthermore, the simulated flow field structure validates the theoretical flow field diagram derived from experimental data reported in the literature. The simulation methodology successfully provides statistically reliable droplet size information. As operating conditions intensify, the droplet size-velocity distribution transitions from an L-shaped pattern to a triangular clump-like configuration. This transition underscores the method's capability to precisely simulate both primary and secondary atomization, along with the intricate evolution and distribution patterns of the atomization field across a diverse range of conditions, with both high speed and precision. Our findings demonstrate that the Eulerian-Lagrangian approach offers a robust framework for understanding and forecasting the complex atomization in liquid rocket engines, advancing atomization tech in aerospace.

The complex interaction between shock waves and two-phase interfaces can generate cavitation. In this study, the cavitation induced by the high-speed jet impact on the water surface was investigated. The mixture fluid is modeled using the barotropic equation of state under the framework of the two-phase flow model, which can describe the mixture of air, water, and vapor with any proportion. Through constructing a 1D Riemann problem for the impact-induced cavitation phase transition, it indicates that the coupling effect of multiple rarefaction waves emitted from the two-phase interface is responsible for the cavitation phase transition inside the liquid. Then, a 3D (three-dimensional) simulation regarding the impact of a high-speed jet on the water surface was conducted and validated against previous experiments that captured the cavitation phase transition phenomenon in the central region after the jet impact. The 3D simulation results revealed the spatial structure and development process of shock waves in detail. The coupling effects of shock waves and two-phase interfaces generate a ring-shaped rarefaction wave, which develops radially inward and superimposes, resulting in the formation of acorn-shaped cavitation bubble nuclei inside the water. The 3D simulation can provide spatial shock/rarefaction wave structures and internal flow details that have never been obtained in experiments, such as shock generation and propagation, rarefaction wave generation and center convergence, and the internal structure of acorn-shaped cavitation nucleation. Furthermore, the influence of the jet velocity on the cavitation intensity was analyzed, and a quantitative relationship was provided.

This study examines self-pulsation spray oscillations in a gas-centered swirl coaxial (GCSC) injector using high-speed photography and numerical simulation. For the first time, high-speed photography captured the unsteady gas–liquid flow inside the GCSC injectors' recess chamber, revealing three spray modes: stable liquid-film breakup, intermittent oscillatory breakup, and purely aerodynamic breakup. Mid- to high-frequency oscillations are governed by the gas–liquid momentum flux ratio and the recess ratio (RR). The core mechanism is a “pressure-relaxation” cycle triggered by periodic gas–liquid blockage in the recess. In this cycle, high-speed airflow expands and compresses the liquid film, causing pressure to build up and then release through the nozzle as a closed-loop oscillation. In stable film-breakup mode at M < 0.1, high-frequency oscillations can arise from Kelvin–Helmholtz waves and viscous shear, even without gas–liquid blockage. Frequency analysis shows that oscillation frequency is closely related to momentum ratio, liquid Reynolds number, and gas Weber number. High-frequency oscillations occur when 0.1 ≤ M < 0.8 and Rel >15 000 (J < 10, Weg < 6000) but disappear when M ≥ 0.8 and Rel < 20 000 (J ≥ 10, Weg ≥ 6000), leaving low- and medium-frequency instabilities. A Strouhal number correlation shows a peak at a recess ratio of 1.4 (∼2–4 kHz), a drop to ∼0.5–2 kHz at RR = 1.7, and no high-frequency oscillations at RR ≈ 1. These findings offer insight into self-pulsation mechanisms and provide guidance for optimizing injector design to mitigate high-frequency combustion instabilities in rocket thrust chambers.