A mechanism stimulating sound production from air bubbles released from a nozzle

Abstract

Gas bubbles in water act as oscillators with a natural frequency inversely proportional to their radius and a quality factor determined by thermal, radiation, and viscous losses. The linear dynamics of spherical bubbles are well understood, but the excitation mechanism leading to sound production at the moment of bubble creation has been the subject of speculation. Experiments and models presented here show that sound from bubbles released from a nozzle can be excited by the rapid decrease in volume accompanying the collapse of the neck of gas which joins the bubble to its parent.

Quantification of undersea gas leaks from carbon capture and storage facilities, from pipelines and from methane seeps, by their acoustic emissions

“…At any given bubble radius measured, there was around an order of magnitude of scatter in values of R 30i /R 0 . They conclusively identified the mechanism for bubble excitation for the shear fragmentation they measured (which would probably resemble excitation during injection or underwater gas pipe leakages) as a volume change in the bubble gas generated by the rupture of the necking region between the future fragments, the energy being manifest at the moment of fragmentation in the surface tension energy associated with the geometry of the neck (Deane & Czerski 2008;Deane & Stokes 2008). Importantly, they predicted that the forcing function was proportional to the internal gas pressure in the bubble, suggesting the possibility that for a given bubble radius the quantity R 30i /R 0 may be broadly invariant with depth (within the limits of the observed scatter, over much of the bubble size range).…”

“…, where G is a ring-up factor evaluated by empirical observation or from the developing theoretical base (Longuet-Higgins 1990;Pumphrey & Ffowcs Williams 1990;Leighton 1994, §3.7.3;Clarke & Leighton 2000;Deane & Czerski 2008). Substitution of (2.5) into (2.3) gives the monopole emission detected in the far field from a single bubble:…”

A candidate mechanism for exciting sound during bubble coalescence

“…Recent research 4 has shown that the sound emitted when a new bubble is formed at a nozzle is consistent with the volume forcing produced by the rapid change in bubble shape just after pinch-off. The collapse of the conical neck of air that had connected the new bubble to the parent gas supply is fast because the radius of curvature of the new surface is very small.…”

“…(9) is due to the form in which the forcing is inserted into the Rayleigh-Plesset equation, as an equivalent external pressure. 4 This forcing term can then be used to drive the linearized Rayleigh-Plesset equation, once the appropriate time dependence is taken into account (discussed below). To apply the Rayleigh-Plesset equation, it is necessary to use an equivalent spherical radius for the new bubble, and we assume here that the breathing mode response of the bubble can be described using spherical symmetry.…”

“…A dynamical model of the volume change on coalescence will be described here, following the principles used in Deane and Czerski. 4 The consequent dynamical and acoustical predictions will be tested against the data published by Thoroddsen et al 5 and Manasseh et al…”