Bubble collapse in complex geometries

Abstract

A gas or vapour bubble near a solid boundary collapses towards the boundary due to the asymmetry induced by the nearby boundary. High surface pressure and shear stress from this collapse can damage, or clean, the surface. The majority of prior research has focused on simple flat boundaries or cases with limited complexity. In this research, we experimentally and numerically investigate how complex geometries affect bubble collapse dynamics. We first investigate how a slot in a flat boundary affects the jet direction for a single bubble. We use a boundary element model to predict how the jet direction depends on key geometric parameters and experimentally validate the predictions using laserinduced cavitation. We reveal a tendency for the jet to be directed away from a slot. Various bubble collapse properties, such as bubble displacement and rebound size, have been shown to be a function of the ‘anisotropy’ of the collapse, measured by a dimensionless representation of the Kelvin impulse known as the anisotropy parameter [Supponen et al., J. Fluid Mech. 802, 263-293 (2016)]. However, characterisation of the anisotropy parameter in different geometries has been limited to simplified analytic solutions. We further develop our boundary element model to be capable of predicting the anisotropy parameter for any rigid complex geometry. We experimentally explore a robust measure of bubble displacement, showing that the bubble displacement in a range of complex geometries behaves as a single function of the predicted anisotropy parameter values. We then extend this model, in combination with experiments, to the study of porous plates by investigating how the standoff distance, porosity, pore size, and pore shape affect two collapse properties: bubble displacement and bubble rebound size. We show that these properties depend primarily on the standoff distance and porosity of the boundary and show that they each collapse onto respective single curves. This work provides key insights into the effects of complex geometries on bubble collapse behaviour. The numerical model developed herein provides a simple, inexpensive method to connect complex geometries to the growing framework of studies using the anisotropy parameter.

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Identifiers

ORCID for Elijah Andrews: orcid.org/0000-0002-4634-199X

ORCID for Ivo Peters: orcid.org/0000-0002-3549-3322

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