Transient dynamics of viscous drop impact on immiscible liquid bath: A holistic analysis*

Droplet entry problems offer extensive opportunities to understand the non-trivial multifluid interaction and the resulting complex evolution of phase boundary. Although droplet entry problems on identical or miscible liquid pool has been prolifically studied, its immiscible counterpart is rather unexplored. In this work, we present our holistic approach coupling experimental observation with theoretical and numerical validation to better understand the dynamics of droplet impact for an oil droplet impinged on a water pool. Our focus is laid on understanding the topologically complex temporal evolution of the oil/water liquid interface. Images acquired from a high-speed camera has been processed to obtain the interface acceleration which in turn is used to calculate an assistive force field responsible for the pinch-off. An analysis involving the change in total energy in the penetration process for a flow field with negligible viscous dissipation has been presented. The experimental results are validated with a volume of fluid based numerical model developed in-house. Additionally, we investigated the equilibrium droplet shape beyond penetration and its dependence on the properties of surrounding fluid, which still is an unexplored area in literature.