Non-axisymmetric flow characteristics in Head-on Collision of Spinning Droplets

TL;DR

This study uses numerical simulations to explore how spinning droplets affect collision dynamics, revealing non-axisymmetric flow features, energy transfer, and enhanced mixing during head-on droplet collisions.

Contribution

It is the first detailed numerical investigation of non-axisymmetric flow effects caused by droplet spinning in head-on collisions.

Findings

Spinning droplets induce non-axisymmetric flow features.

Spinning motion promotes droplet mass interminglement.

Non-axisymmetric flow increases with orthogonality of motions.

Abstract

Effects of spinning motion on the bouncing and coalescence between a spinning droplet and a non-spinning droplet undergoing the head-on collision were numerically studied by using a Volume-of-Fluid method. A prominent discovery is that the spinning droplet can induce significant non-axisymmetric flow features for the head-on collision of equal-size droplets composed of the same liquid. Specifically, a non-axisymmetric bouncing was observed, and it is caused by the conversion of the spinning angular momentum into the orbital angular momentum. This process is accompanied by the rotational kinetic energy loss due to the interaction between the rotational and radial flows of the droplets. A non-axisymmetric internal flow and a delayed separation after temporary coalescence were also observed, and they are caused by the enhanced interface oscillation and internal-flow-induced viscous dissipation. The spinning motion can also promote the mass interminglement of droplets because the locally non-uniform mass exchange occurs at the early collision stage by non-axisymmetric flow and is further stretched along the filament at later collision stages. In addition, it is found that the non-axisymmetric flow features increase with increasing the orthogonality of the initial translational motion and the spinning motion of droplets.