Evolution of the gas-liquid interface dominated by Richtmyer-Meshkov instability

As injection pressure for diesel spray increases, the Richtmyer-Meshkov (RM) instability increasingly impacts the interface, which dominates the deformation and breakup of the liquid interface together with the Rayleigh–Taylor (RT) instability, the Kelvin–Helmholtz (KH) instability, and turbulence, thus the breakup of sprays. Study on the gas-liquid instability dominated by RM instability is important to reveal the multiphase flow coupling in the nozzle and mechanism of the primary breakup. In this paper, a high-precision code for two-phase flow is proposed and its reliability is verified. Then the mechanism of interface evolution under high-speed airflow with the impact of RM instability is explored. The experimental and numerical methods were employed. It was found that the evolution of the gas-liquid interface can be divided into two stages according to the relative positional relationship between the shock wave and the droplet. In the first stage, the initial shock wave intersects with interface of droplet, and the reflected and refractive patterns of the shock wave change with the varying angle between the shock wave and the interface. The change of the pressure distribution and the accumulation of baroclinic vorticity at the interface play essential roles in the instability and deformation of the droplet after the initial shock wave separates from the droplet interface. In the second stage, the droplet surface gradually forms the structure of the spikes and bubbles, and the airflow with different velocities significantly influences the morphology of the droplets during the breakup, causing different breaking patterns.