A vortex ring bubble crossing an oil-water interface

The dynamics of a vortex ring bubble passing vertically through an oil-water interface are experimentally investigated. The vortex ring bubble is generated by compressed air ejected through an orifice in water for a short period of time. The volume of the vortex ring bubble is controlled via the pressure and ejection time of the compressed air. High-speed imaging is used to examine the evolution of the vortex ring bubble and its interaction with the interface. The vortex ring bubble entrains surrounding water, and this entrainment process strongly affects the dynamics of the vortex ring bubble near the interface. The interaction observed at the interface shows notable differences from the interaction between a single-phase vortex ring and a density interface. Throughout the upward motion of the vortex ring bubble, kinematic properties such as the radius and velocity of the bubble are primarily determined by the relative magnitude between the buoyant force of the bubble and the gravitational force acting on the entrained volume of water. We investigate key dimensionless parameters, including the Froude number, that can characterize the dynamics of the interface.