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 deforma-tion 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 theWe-ber number (We) on the evolution process. Four dimensionless droplet-wall distances (once shocked: L/d0 = 1; 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 ele-vated from 50 to 3592, which was because the higherWe 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.