Experiments on the breakup and evaporation of small droplets at high Weber number

Abstract

Shock-driven multiphase mixing is present in numerous physical systems such as detonation-driven propulsion engines, liquid–vapor cloud explosions, and hypersonic flight droplet impacts. At the microscale, droplets experience deformation, breakup, and evaporation under extreme conditions (high Weber and Reynolds regimes). For small droplets, these phenomena are simultaneous and highly transient, making their interactions and interdependencies warrant further investigation. In this study, experiments are conducted in a shock tube facility to investigate these simultaneous droplet-scale phenomena. An interface consisting of small acetone droplets (⌀ 10–40 [μm]) is impulsively accelerated by a strong planar shock wave (Mach ∼2.09). The droplet size distribution is well-characterized in-situ utilizing a Phase Doppler Particle Analyzer (PDPA) and shadowgraphy. The development of child droplet clouds is captured through an ensemble of Mie scattering images. A simplified model is developed to interpret the experimental results, combining deformation, breakup, and evaporation models. The results indicate that the breakup of small droplets at high Weber numbers is likely dominated by the Rayleigh–Taylor (RT) mechanism, aligning with previous empirical models for low Weber numbers.