The interaction of a droplet with an immiscible deep liquid pool for density ratio greater than unity

Abstract

Droplet interaction with liquid pools has been widely studied. The focus of these studies has primarily been on like-fluids, the droplet being miscible with the pool. Such miscible droplet–pool interactions have been extensively studied for their regimes of Rayleigh jet formation, crater formation, splashing, and coalescence. However, the case of immiscible droplet fluid has received considerably less attention from researchers. The immiscible case is relatively complex to understand owing to the involvement of three interfacial tensions. In the current study, we investigate the regimes of droplet–pool interaction for the case of immiscible droplet fluid having higher density and surface tension than pool fluid. Droplet properties are characterized through Weber number while Ohnesorge number is used to characterize pool fluid. Weber number is controlled through velocity of droplet and viscosity of pool is used to predict Ohnesorge number. Validating the numerical methods with experimental data, extensive numerical simulations are performed to gain insight into droplet–pool interaction. Current investigation reveals that for the case of immiscible fluids, regime formation is observed due to Rayleigh–Plateau instability as well as droplet fluid interacting with the pool fluid. This enables the pool fluid jet separation at high Ohnesorge numbers too, in contrast to miscible fluids case. The regimes of droplet–pool interaction for current case are described in detail and classified over wide range of Weber and Ohnesorge numbers.