Oscillations of a gas pocket on a liquid-covered solid surface

Abstract

The dynamic response of a gas bubble entrapped in a cavity on the surface of a submerged solid subject to an acoustic field is investigated in the linear approximation. We derive semi-analytical expressions for the resonance frequency, damping and interface shape of the bubble. For the liquid phase, we consider two limit cases: potential flow and unsteady Stokes flow. The oscillation frequency and interface shape are found to depend on two dimensionless parameters: the ratio of the gas stiffness to the surface tension stiffness, and the Ohnesorge number, representing the relative importance of viscous forces. We perform a parametric study and show, among others, that an increase in the gas pressure or a decrease in the surface tension leads to an increase in the resonance frequency until an asymptotic value is reached

Enhancing acoustic cavitation using artificial crevice bubbles

“…The driving frequency is approximately twice the linear resonance frequency (98 kHz) of the pit and lies below the first higher harmonic of 243 kHz [36]. Similar to previous observations, there is a threshold for the pressure above which bubble pinch-off occurs corresponding to an input power of 50 mW.…”

“…In comparison, the resonance frequencies for the first and second surface mode for this pit are 139 kHz and 276 kHz respectively, based on linear potential flow analysis [36]. This explains the larger amplitude response of the pit bubble compared to that of the ejected bubbles.…”

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