Impact of non-spherical droplets onto a liquid pool*

Droplets larger than the capillary length either released from a needle or generated from any other mechanism are not perfectly spherical and show significant variations in their axis ratio after release. Variations in the droplet axis ratio may significantly affect the depth of cavity penetration, shape, and formation-retraction time. We investigate crater evolution and crater shape formed by the impact of very large non-spherical droplets onto a deep liquid pool theoretically as well as experimentally. Both a droplet impact energy balance and a potential flow model are proposed to predict the effect of droplet axis ratio on the crater shape. Experimental results show that the droplet shape at impact significantly change the crater shape and evolution time. Prolate droplets make deep-narrow craters and oblate droplets make shallow-wide craters. The time of cavity formation and retraction is short for prolate and long for oblate shaped droplet impacts. The energy model reveals that the cavity aspect ratio scales parabolically with the droplet axis ratio. The potential flow model predicts cavity evolution time for different droplet shapes with good experimental agreement.