THE EFFECT OF THE WEBER NUMBER ON THE DROPLET DEFORMATION AND BREAKUP PROCESS BEFORE A STANDING WALL

Twice-shocked interaction phenomena are frequently observed in engineering in scenarios where the passageway of the shock wave contains obstacles. In this work, the transient droplet deformation and breakup behaviors induced by a shock wave before a standing wall were first experimentally recorded using a high-speed background technique. Special attention was paid to the effect of the Weber number (We) on the evolution process. Four dimensionless droplet-wall distances (once shocked: L/d0 = ∞; twice shocked: L/d0 = 3, 1, and 0.6) were involved, along with We ranging from 50 to 16,770. The results showed that compared with the once-shocked experiments, the deformation and breakup behaviors of the twice-shocked experiments varied greatly due to the rather complex flow conditions. Many new deformation and breakup features such as a hat shape and multi-sheets were observed. The dimensionless cross-stream diameter (dc/d0) increased over time for all cases, while the oscillation and flat disc phenomena appeared in some twice-shocked cases. The growth rate of dc/d0 increased with the We in both the once- and twice-shocked experiments. Owing to the accelerated breakup process, with an increase in the We the maximum of the dimensionless droplet cross-stream diameter (dc/d0)max decreased in the once-shocked experiments. The variation trend of (dc/d0)max varied with L/d0. For the L/d0 = 3 cases, the value of (dc/d0)max first increased and then decreased with the We since the increased We changed the breakup behaviors. For the L/d0 = 1 and 0.6 cases, the value of (dc/d0)max increased with the We when the We was elevated from 50 to 3592, which was because the higher We cases had more time to acquire energy from the outside. For the twice-shocked experiments, the droplets oscillated at their natural frequency for different values of L/d0 and We.