Spray dynamics and time-lag effects during high-pressure liquid oxygen impinging jets atomization without or with pressure oscillations

This study numerically investigates the spray dynamics and time-lag effects in high-pressure liquid oxygen (LOX) impinging jet atomization under three scenarios: varying pressure differences without oscillations, upstream pressure oscillations with different amplitudes, and downstream pressure oscillations. By coupling the Volume of Fluid method with the Lagrangian Particle Tracking model, the atomization process—encompassing liquid sheet breakup, fragment formation, and droplet generation—is analyzed through high-fidelity simulations. The results show that, in the absence of pressure oscillations, increasing the pressure difference influences jet velocity and droplet mass flow rate but has minimal effect on the Sauter Mean Diameter (SMD) within the considered range. Even without oscillations, the droplet mass flow rate exhibits large, nonperiodic fluctuations, reflecting the intrinsic instability of the atomization process, which may contribute to combustion instability. When external pressure oscillations are applied, either at the injector inlet or combustion chamber outlet, periodic variations are induced in both mass flow rate and SMD of the generated droplets. The amplitude of oscillation is positively correlated with the intensity of pressure fluctuations. Additionally, time-lag phenomena are observed: there is a negligible time lag between pressure oscillations and LOX mass flow rate fluctuations, while significant delays are seen between LOX mass flow rate and droplet mass flow rate oscillations. The time lag between LOX mass flow rate and SMD oscillations is comparatively shorter. These findings provide insights into transient spray behavior and temporal correlations in high-pressure impinging jet atomization, aiding the optimization of injector designs and improving combustion stability in rocket engines.