Distribution and mixing mechanism of a liquid jet injected in the tandem backward-facing step cavity in supersonic flow

Mixing process and flow field structures of liquid jet in high speed crossflow (Mach = 2) in the tandem backward-facing step cavity combustion chamber were investigated numerically. The Eulerian–Lagrangian method coupled with Kelvin–Helmholtz/Rayleigh–Taylor instability breakup model was employed in the simulation. Effects of the position of the backward-facing step and the length of the backward-facing step on droplet mixing in the cavity were studied. The simulation results showed good agreement with experimental data. It was revealed that in high speed crossflow, the jet atomization region can be roughly divided into three regions: the mainstream region, the cavity recirculation region, and the backward-facing step recirculation region. According to the flow mode in the cavity, the cavity recirculation region can be divided into four modes: open cavity (mode I), closed cavity (mode II), open cavity with reattachment shock wave uplift (mode III), and closed cavity with reattachment shock wave uplift (mode IV). The number of droplets entering the cavity is lower in modes I and III compared to modes II and IV, where a greater number of droplets enter the cavity.