Low‐frequency acoustic emissions by impacting transient cylindrical water jets in fresh and salt water

The impact of a jet of water onto a still water surface results in the entrainment of large amounts of air and the eventual formation of a bubble plume. The densely populated bubble plumes were generated by dropping a fixed volume of water, held in a cylindrical container, onto a still‐water surface. The detached bubble plume, which is roughly spherical in shape, undergoes volume pulsations and radiates relatively large‐amplitude, low‐frequency sound. The results of laboratory study of the noise produced by this process were reported previously by Kolaini et al. [J. Acoust. Soc. Am. 89, 2452–2455 (1991)]. In this presentation, a field study of noise produced by this process in both fresh water (Lake Washington) and salt water (the Puget Sound) will be described. Studies of acoustic emissions from transient bubble plumes as a function of cylinder parameters will be described, with specific attention devoted to a comparison of results obtained in salt and fresh water. The measurements indicate that there is a correlation between the acoustic intensity radiated from bubble plumes and the total potential energy of the water jet. [Work supported by ONR.]