Dynamical behavior of an oscillating bubble initially between two liquids.

The interaction of an oscillating bubble and a nearby liquid–liquid interface is a complex multiphase problem that has many potential applications. In this work, the behavior of a bubble initially between two different liquids (i.e., with a stand-off distance of zero) is investigated numerically and is shown to exhibit a high degree of nonlinearity. A numerical model based on an Eulerian finite-element method is established. It is validated by simulating a nonspherical collapse of a bubble in the gravity field and comparing the results with those obtained in the experiment. Then, several cases of interaction between an oscillating bubble and a liquid–liquid interface are simulated with different initial conditions. It is confirmed that the density interface tends to induce the bubble to develop a jet that drills into the heavier liquid during the bubble collapse phase. The nondimensional period of oscillation increases with increasing density ratio of the two liquids, and an annular jet impacts, generating a pressure peak, when the density ratio exceeds 1.5. When the effect of gravity is taken into account, it is found that the annular impact is enhanced while the downward jet is weakened. In addition, a significantly sized bubble is split from the main bubble by the impact of the annular jet. When the buoyancy parameter exceeds a threshold value, gravity comes to dominate the bubble motion, and neither an annular jet nor a downward jet will develop. If the buoyancy parameter is large enough, the bubble migrates upward and detaches from the liquid–liquid interface during the collapse phase. [ABSTRACT FROM AUTHOR]