Study Reveals Complex Rise Dynamics of Droplets in Immiscible Liquids
Researchers used direct numerical simulations to map the full sequence of rise behaviors exhibited by toluene droplets ascending through water, uncovering multiple distinct dynamical regimes as droplet size increases. The study focused on a moderate drop-to-fluid viscosity ratio and varied droplet radius from 0.5 mm to 3.0 mm. The findings show that moderate-viscosity droplets follow a fundamentally different path-instability mechanism than bubbles or solid particles, with symmetry breaking originating inside the droplet rather than in the surrounding wake.
A new preprint posted to arXiv investigates how buoyant toluene droplets rise through clean water using both axisymmetric and fully three-dimensional direct numerical simulations. As droplet radius increases from 0.5 mm to 3.0 mm, the system passes through a rich sequence of regimes: steady vertical rise, an internal flow instability with an azimuthal mode m=2 that reduces terminal speed, a steady oblique regime where m=1 and m=2 modes coexist, a near-vertical phase, a rotating-wave regime with constant azimuthal drift, and finally fully chaotic three-dimensional paths driven by shape oscillations and vortex shedding. Simulations initialized from finite-amplitude asymmetric states also reveal several size ranges where multiple stable terminal states coexist depending on initial conditions, a phenomenon known as multistability. A key finding is that axisymmetry breaking is initiated by instabilities within the droplet's internal flow, rather than in the external wake as is typical for bubbles and solid particles. This distinction highlights the critical role of the viscosity ratio in governing droplet dynamics and has implications for industrial and natural processes involving liquid-liquid systems.
What's missing
As a preprint, this work has not yet undergone peer review, so results should be treated as preliminary. The study is limited to a single viscosity ratio (μ* = 0.62, toluene in water) and clean-interface conditions; surfactant effects, contamination, and other viscosity ratios are not addressed. Generalizability to other liquid-liquid systems or to experimental validation remains an open question.
What different sources said
- arXiv physicsCenter
Impact Dynamics of Droplet Containing Particle Suspensions on Deep Liquid Pool
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