The release of air bubbles from an underwater nozzle

Abstract

Air bubbles released from an underwater nozzle emit an acoustical pulse that is of interest both for the study of bubble detachment and for elucidating the mechanism of sound generation by a newly formed bubble. In this paper, the sequence of bubble shapes is calculated theoretically from a given nozzle, and it is shown that there is for each nozzle a bubble of maximum volume Vmax. Assuming that the bubble becomes detached at its “neck,” and that the volume of the detached bubble equals the volume V* of the undetached bubble above its “neck,” it is determined for each nozzle diameter D an acoustic frequency f* corresponding to “slow” bubble release. Experiments show that the acoustic frequency, hence the bubble size, depends on the rate of air flow to the bubble, but for slow rates of flow the frequency f is very close to the theoretical frequency f*. High-speed photographs suggest that when the bubble pinches off, the limiting form of the surface is almost a cone. This is accounted for by assuming a line sink along the axis of symmetry. Immediately following pinch off, there is evidence of the formation of an axial jet going upward into the bubble. This may play a part in stimulating the emission of sound.

Consideration of the dynamic forces during bubble growth in a capillary tube

“…Other studies observed bubble growth and shape from appearance in the tip of an orifice or capillary tube until detachment (Kupferberg and Jamenson, 1969;Pinczewski, 1981;Gaddis and Vogelpol, 1986;Tsuge, 1986;Longuet-Higgins et al, 1991;Oguz and Prosperetti, 1993;Teresaka and Tsuge, 1993;Sundar and Tan, 1999;Hé brard, 2003, 2004). However, detailed observations of the bubble formation process from appearance at the capillary tube tip through detachment are lacking in the literature.…”

Experimental investigation on the breakup dynamics for bubble formation in viscous liquids in a flow-focusing device

“…In Fig It is worth noting that there is a 2/5 or 1/2 scaling exponent after the 1/3 -scaling as reported in Ref (Lu et al, 2014a;van Hoeve et al, 2011) as demonstrated in Table 1, which is not observed in this study. In addition, the exponent of 1/3 is smaller than 1/2 that was observed for bubble formation in a static low viscosity liquid in a large container without confining boundaries, for which the breakup was predominated by the inertial forces (Burton et al, 2005;Gekle et al, 2009;Longuet-Higgins et al, 1991;Thoroddsen et al, 2007). …”

Flow structures of gaseous jets injected into water for underwater propulsion

“…The Rayleigh-Plesset equation can not predict the break-up because it assumes that expansion is confined in the radial direction homogenously. As a result, the details of flow physics and development can not be captured, and this bubble model is more suitable for a low-speed jet [14,15]. For a high-speed jet, the Navier-Stokes equation is a better candidate to numerically assess the flow structures.…”