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The pulsating bubble near different boundaries demonstrates various dynamics. In this study, the three-dimensional Eulerian finite element method with the adaptive mesh refinement technique was used to investigate the interaction between a bubble and a free surface near a solid wall, including the toroidal bubble motion after the jet impact. The impact pressure on the solid wall was investigated, and the changing trend of pressure peak reverses when the initial depth of the bubble center is between 0.7 and 0.9 times the bubble's maximum radius. Throughout the process, competition occurs between the Bjerknes effects of the free surface and solid wall, which leads to the nonspherical pulsation of the bubble. Different collapsing forms of bubbles, i.e., the strong jet, weak jet, and crescent-type forms, were identified. Greater depth may result in a reduced height of a free surface water column, which is described in a fitting curve. Additionally, inclination of the solid wall can cause the free surface to exhibit a side hump or groove phenomenon. But for a large-scale bubble, no groove phenomenon of the free surface occurred, and the bubble collapsed in a horn-shaped form with two jets in the upward and downward directions. [ABSTRACT FROM AUTHOR]

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]