Experiments on the fragmentation of a buoyant liquid volume in another liquid

TL;DR

This paper investigates how a heavier, buoyant liquid fragmentizes when released into a lighter immiscible liquid, exploring various fragmentation regimes influenced by fluid dynamics instabilities and turbulence at different Weber numbers.

Contribution

The study provides experimental insights into fragmentation processes of buoyant liquids, adapting turbulent entrainment theory to immiscible fluids and identifying regimes based on Weber number variations.

Findings

Fragmentation involves Rayleigh-Taylor instability and vortex ring dynamics.

Turbulent entrainment theory applies to buoyant vortex rings in immiscible fluids.

Different regimes are observed depending on Weber number, from stable deformation to turbulence.

Abstract

We present experiments on the instability and fragmentation of volumes of heavier liquid released into lighter immiscible liquids. We focus on the regime defined by small Ohnesorge numbers, density ratios of order one, and variable Weber numbers. The observed stages in the fragmentation process include deformation of the released fluid by either Rayleigh-Taylor instability or vortex ring roll-up and destabilization, formation of filamentary structures, capillary instability, and drop formation. At low and intermediate Weber numbers, a wide variety of fragmentation regimes is identified. Those regimes depend on early deformations, which mainly result from a competition between the growth of Rayleigh-Taylor instabilities and the roll-up of a vortex ring. At high Weber numbers, turbulent vortex ring formation is observed. We have adapted the standard theory of turbulent entrainment to buoyant vortex rings with initial momentum. We find consistency between this theory and our experiments, indicating that the concept of turbulent entrainment is valid for non-dispersed immiscible fluids at large Weber and Reynolds numbers.