A study on “Dynamics of internal jets in the merging of two droplets of unequal sizes” conducted by Dr Peng Zhang, Assistant Professor of Department of Mechanical Engineering has recently been published on the Journal of Fluid Mechanics.
The dynamics and interactions of liquid droplets, particularly droplet collision, are of essence to numerous natural and industrial processes such as rain clouds and rocket engines. To date, most research has focused on discovering various collision outcomes – the droplets may bounce off, or coalesce with tiny or large deformation, or separate after temporary coalescence – and unraveling the physics underneath these outcomes.
In a new work on droplets of unequal size, Dr Peng Zhang and his team, collaborating with colleagues at Princeton, Tsinghua and Xi’an-Jiaotong universities, have experimentally discovered a new phenomenon regarding the fate of the liquids – jet-like mixing patterns emerge when the collision is either weak or strong, but disappear in between – within the permanently coalesced droplet. The team’s computer simulation, validated experimentally, reveals why: the jet formation upon weak droplet collision is driven by the large capillary pressure of the smaller droplet; it is suppressed by the substantial droplet deformation when the collision is moderately strong; it reemerges because of the droplet stretching in the direction of sufficiently strong collision. This work was recently accepted to be published on the Journal of Fluid Mechanics. [C. Tang, J. Zhao, P. Zhang, C. K. Law, and Z. Huang, J. Fluid Mech. (2016), vol. 795, pp. 671-689]