Dynamics of air bubbles passing through a liquid-liquid interface

The passage of rising air bubbles through an initially flat horizontal liquid-liquid interface is studied using both laboratory experiments and Direct Numerical Simulation. The dynamics of spheroidal, spherical cap and toroidal bubbles near the liquid-liquid interface and subsequently through the upper liquid are investigated by coupling high-speed shadowgraph visualizations and Particle Image Velocimetry techniques. Axisymmetric computations are also carried out to assess the validity of presently available computational approaches in three-phase flows. These computations are based on two distinct approaches, namely a Volume Of Fluid approach without interface reconstruction and a Cahn-Hilliard model coupled with the incompressible Navier-Stokes equations. Experimental and computational results are compared in various configurations, including cases where the bubble is trapped at the liquid-liquid interface or rises in the upper phase while towing a column of the lower liquid that eventually breaks into droplets of various sizes.