Abstract
We experimentally, numerically and theoretically investigate the nonlinear interaction between a cavitation bubble and the interface of two immiscible fluids (oil and water) on multiple time scales. The underwater electric discharge method is utilized to generate a cavitation bubble near or at the interface. Both the bubble dynamics on a short time scale and the interface evolution on a much longer time scale are recorded via high-speed photography. Two mechanisms are found to contribute to the fluid mixing in our system. First, when a bubble is initiated in the oil phase or at the interface, an inertia-dominated high-speed liquid jet generated from the collapsing bubble penetrates the water–oil interface, and consequently transports fine oil droplets into the water. The critical standoff parameter for jet penetration is found to be highly dependent on the density ratio of the two fluids. Furthermore, the pinch-off of an interface jet produced long after the bubble dynamics stage is reckoned as the second mechanism, carrying water droplets into the oil bulk. The dependence of the bubble jetting behaviours and interface jet dynamics on the governing parameters is systematically studied via experiments and boundary integral simulations. Particularly, we quantitatively demonstrate the respective roles of surface tension and viscosity in interface jet dynamics. As for a bubble initiated at the interface, an extended Rayleigh–Plesset model is proposed that well predicts the asymmetric dynamics of the bubble, which accounts for a faster contraction of the bubble top and a downward liquid jet.
Highlights
Bubble dynamics is a typical multiphase flow problem, which has received much attention for many years due to its broad applications and interesting behaviours (Prosperetti 2004; Lauterborn & Kurz 2010; Lohse 2018)
In the experiments discussed above, we find that the interface evolution is closely related to the bubble motion during the first cycle of the bubble
Since the bubble jet penetration into the water–oil interface is an important mechanism of emulsification or fluid mixing, especially the formation of very fine droplets, here we quantitatively study the jet dynamics for bubbles initiated in oil
Summary
Bubble dynamics is a typical multiphase flow problem, which has received much attention for many years due to its broad applications and interesting behaviours (Prosperetti 2004; Lauterborn & Kurz 2010; Lohse 2018). Chahine & Bovis (1980) performed experiments for spark-generated bubbles near the interface of two immiscible liquids They discussed the dependence of the bubble jet direction on the standoff parameter and the Froude number since their motivation was cavitation damage reduction. Matsutaka & Komarov (2021) experimentally studied the dynamics of acoustic cavitation bubbles near a gallium droplet interface. Liu et al (2019) proposed a volume of fluid model implemented in the finite element method to study the behaviour of a bubble generated at the interface of two different liquids They revealed the role of gravity and density ratio of the two fluids in bubble migration and jet direction. Yamamoto & Komarov (2020) numerically studied the jet dynamics of acoustic cavitation bubbles near a gallium droplet using a commercial software.
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