Large-droplet deep-pool impact: larger isn't necessarily better

The shape of a droplet impact onto a liquid pool may greatly influence the dynamics of the cavity formation and splashing. Although droplet impact onto a liquid pool has been investigated for relatively small droplets, behaviors greatly change when the droplet is large enough that significant oscillation deformation occurs. We experimentally investigate large droplet impact (1 to 6 cm dia.) onto a deep pool of water. Droplet release height is selected to cover a larger range of Weber numbers from 10² to 10⁵. The droplets oscillate significantly when diameters are larger than the capillary length. The shape and dynamics of the cavity formed by the large droplets are significantly affected by the deformation of the droplet at impact. In general, three different shapes of the impacting droplets occur: prolate, oblate and circular. We show that, for a fixed liquid volume and a fixed Weber number of an impacting droplet, prolate shaped droplets produce the maximum cavity depth whereas an oblate shaped droplet results in a minimum cavity depth. The ratio of cavity width to maximum cavity depth (cavity aspect ratio) is a function of the horizontal diameter of the droplet at impact. Increased horizontal diameter results in a reduced impact energy flux leading to reduced cavity depth.