Numerical investigation on atomization of multiple jets impinging at an annular liquid film with elevated gas-to-liquid density ratio

Bi-propellant atomization of pintle injector is modeled as multiple jets (oxidizer) impinging an annular liquid sheet (fuel). Numerical simulation of the atomization behaviors is conducted at elevated gas to fuel density ratios with coupling Eulerian–Lagrangian approach. A dual-loop tagging algorithm is proposed to identify the droplets without additional mesh refinement. Our results show that for all density ratio cases investigated here, the atomization field can be characterized by three regions quantified by mass fraction (mixing, transition and falling region). These regions have significantly different droplet size and mixing ratio distributions. SMD decreases in the mixing region, but in the transition and falling region, SMD firstly increases and then decreases. Furthermore, at low density ratio, the mixing ratio presents the unimodal variation trend, while at high density ratio, the mixing ratio presents the bimodal mode. To interpret the effect of the density ratio on the above observations, the continuous mixing sheet and the falling sheet breakup, as well as the discrete droplet coalescence mechanism is analyzed and it is found that higher density ratio leads to advanced breakup of liquid sheets in both mixing and falling regions, which generates more discrete ligaments or droplets in the transition region. However, on the other hand, at sufficiently high density ratio, the discrete ligaments and droplets are so populated that their coalescence mechanism is speculated to be effective, leading to larger sized discrete liquid structures and bimodal variation of mixing ratio.