Entrapment and interaction of an air bubble with an oscillating cavitation bubble

Karri, Badarinath and Sahu, Kirti Chandra and Y S, Kannan (2019) Entrapment and interaction of an air bubble with an oscillating cavitation bubble. In: 72nd Annual Meeting of the APS Division of Fluid Dynamics, 23–26 November 2019, Seattle, Washington.

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Abstract

The mechanism of the formation of an air bubble due to an oscillating cavitation bubble in its vicinity is reported from an experimental study using high-speed imaging. The cavitation bubble is created close to the free surface of water using a low-voltage spark circuit comprising two copper electrodes in contact with each other. Before the bubble is created, a third copper wire is positioned in contact with the free surface of water close to the two crossing electrodes. Due to surface tension at the triple point (wire-water-air) interface, a small dip is observed in the free surface at the point where the wire is immersed. When the cavitation bubble is created, the bubble pushes at the dip while expanding and pulls at it while collapsing. The collapse phase leads to the entrapment of an air bubble at the wire immersion point. During this phase, the air bubble undergoes a `catapult' effect, i.e., it expands to a maximum size and then collapses with a microjet at the free surface. A parametric study is also conducted to understand the effects of wire orientation, bubble distance from the free surface and radius of the bubble on this phenomenon.

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