Experimental Study of Sound Propagation Through Bubbly Water: Comparison With Optical Measurements

The study of the acoustical properties of bubbly flows remains a challenge for scientists. Classical theoretical results provide the expression of a complex effective wave number characterizing sound propagation through such a medium. Theoretical attenuation and phase-speed changes of sound can be obtained from this effective wave number and are specifically observable around characteristic frequencies related to the size of the bubbles. With the aim to contribute to the ongoing research, this paper presents experimental work conducted in a large laboratory tank, to study sound propagation through bubbly water. An original bubble generation technique and the characterization of the generated bubbles by both acoustical and optical methods are reported. In the experiments of this work, air bubbles are injected, using a high-pressure washer, into a large water-filled tank through which sound signals are propagated. The characteristic frequencies and the bubble sizes are determined from the measurements of the sound attenuation and the sound phase speed. These measurements are complemented by concurrent acquisitions of acoustic signals and optical images. A comparative study is conducted between the bubble size distributions deduced from the optical and those deduced from the acoustical measurements.