Effects of radial orifice shapes on spray characteristics of liquid–liquid pintle injector element

The effects of circular, rectangular, and T-shaped radial orifices on the spray characteristics of a liquid–liquid pintle injector element were numerically investigated using the volume of fluid (VOF) method with adaptive mesh refinement (AMR). The high-pressure region near the liquid film–jet impingement point and the growth of Kelvin–Helmholtz (K-H) instabilities were identified as critical factors governing the spray angle and atomization behavior. The formation mechanisms of liquid sheets, ligaments, and droplets from both the film and jet were analyzed. An arched cloak-like sheet was observed to develop due to inertial spreading following deformation induced by film–jet impingement. Ligaments originated from either the growth of K-H instability waves or from perforated holes in the liquid sheets, while droplets were generated through ligament breakup and tearing at sheet edges. Furthermore, the geometric configuration of the radial orifices strongly influenced jet deformation and the topology of instability-driven breakup, thereby determining the spatial distribution of the resulting droplets. Spray characteristics, including spray angle and droplet size, were evaluated. Under identical jetting area and mass flow rate, the orifice shape had only a minor effect on the droplet size. However, T-shaped orifices produced a smaller spray angle and a higher fraction of small droplets compared with circular and rectangular orifices.