Bubble eruptions in a multilayer Hele-Shaw flow

Area of Science:

• Fluid dynamics
• Multiphase flow
• Hele-Shaw cell dynamics

Background:

• Studying fluid behavior in confined geometries is crucial for understanding complex interfacial phenomena.
• Gravitational instability drives fluid rearrangement in layered systems.

Purpose of the Study:

• To investigate the dynamical rearrangement of gravitationally unstable multilayer fluids in a Hele-Shaw cell.
• To classify various stirring and breakthrough dynamics, and characterize air-finger eruptions.

Main Methods:

• Utilized a Hele-Shaw cell with four immiscible fluid layers (air, olive oil, water-glycerin, perfluorohexane).
• Varied fluid properties (viscosity) and layer thicknesses.
• Employed high-speed video to capture and analyze fluid dynamics, including eruptions, wetting, and contact lines.

Main Results:

• Observed distinct dynamics including stirring, layer breakthrough, and counterflows against buoyancy.
• Documented prominent air-finger eruptions through high-viscosity layers, forming hemispherical shapes and generating droplet sprays via neck pinch-off.
• Identified significant roles of wetting, contact lines, and three-dimensionality in eruption dynamics.
• Noted that droplet motion is influenced by both local viscosity and density gradients.

Conclusions:

• The study reveals complex, often counterintuitive, fluid behaviors in layered Hele-Shaw systems.
• Air-finger eruptions and subsequent droplet formation are key phenomena driven by interfacial and viscous forces.
• Layer interchange and overturning dynamics occur on longer timescales, influenced by multi-phase interactions.