Vortex ring interaction with liquid interfaces: A study of a drop formation process.

Abstract

The interaction of a vortex ring with one or two interfaces between immiscible liquids has been studied experimentally. The effects of interface properties and vortex ring strength on the interaction were determined. It was found that the interaction between a vortex ring and a liquid interface can result in drop formation. The existence of critical flow conditions for the occurrence of breakup was established. Drops were formed for Weber numbers above 40 and Froude numbers above 10. An Ohnesorge number effect on the value of the critical Weber number was also observed. The number of drops formed, and the drop properties, were found to depend on the vortex ring properties, as well as on the properties of the liquid interface. Observations of a rebound vortex generated at the interface are reported. PIV measurements for a single liquid interface revealed the development of high vorticity regions due to interface deformation; further, vorticity generated at the interface diffused outside the liquid column and formed a boundary layer, with boundary layer separation observed at some conditions. At low Weber numbers, vorticity generated at the interface diffused into the vortex ring and stopped its motion. Several interaction regimes were identified for the interaction of a vortex ring with two immiscible liquid interfaces, depending on the vortex ring strength and the separation distance between the interfaces. Conditions for creation of a complex encapsulated drop were identified.