Acoustic characterization of a bubble injected into a fully developed turbulent flow field

Abstract

An experiment was designed to investigate the characteristics of sound produced by the turbulent excitation of bubbles. By injecting a bubble into a fully developed turbulent flow, generated by a submerged axisymmetric horizontal water jet, the excitation of bubbles and shear-induced fission/fusion may occur. In the case of shear-induced bubble distortion by a turbulent jet, nonlinear coupling between volume pulsation and surface oscillations occur at exactly the same frequency as the radial breathing mode of the bubble. Particle tracking velocimetry (PTV) is used to characterize the turbulent flow field. Two high-speed Kodak Ekta-Pro video cameras are used to capture, simultaneously, several 180-×180-×10-mm illuminated regions along the jet. An 8-W argon ion laser is utilized for illumination. The method provides not only a visualization of the various patterns and structures of the turbulent flow, but also yields quantitative instantaneous velocity data of the flow containing the bubble. The role of the turbulent flow characteristics in determining the acoustical bubble response is discussed. [Work supported by ONR.]

Broadband parametric imaging of breaking ocean waves

“…15,16 The extent to which these features transfer to spilling breakers is not obvious. Bubbles formed at the forward face of the bore will radiate freely forward and downward into bubble-free water.…”

“…13,14,17 This can also occur in bubble breakup or coalescence. 15,16 The oscillation frequency is inversely related to the bubble radius, a relationship known as the Minnaert formula, 12 and experimental observations 14,18 suggest decay constants of the order of tens of milliseconds for the sizes of bubbles ordinarily encountered in the ocean under natural conditions. Bubble size measurements of the freshly created, ringing bubbles is a problematic task: most early efforts took measurements outside the bubble-creation region, thus measuring the population of ''mature bubbles'' ͑see below͒ rather than that of active, ringing bubbles.…”