Sound channeling through bubbly streams

Abstract

The presence of even small amount of bubbles can have a strong effect on the transmission and reduction of the sound waves through the medium in which they occur. The study presented here examines experimentally and numerically the propagation of acoustic energy in the vicinity of streams of discrete air bubbles. The acoustic energy was created naturally during the detachment of bubbles at the bottom of the stream. Previous work [A. Nikolovska, J. Acoust. Soc. Am. 115, 2473 (2004)] has reported that the root-mean-squared pressure distribution is highly anisotropic in the bubbles vicinity. A new experimental technique has been developed to obtain time frames of the instantaneous acoustic pressure field using two hydrophones. This technique allowed coordinated measurement of the acoustic energy distribution in the near and far field. The results show that the phase speed in the direction of the bubble stream has values considerably lower than the speed of sound in pure water. Different bubble stream configurations were investigated and it was found that this speed of propagation reduces and the quality factor of the sound pulses increases as the air volume fraction in the bubble streams is increased. [Work supported by RCOM.]