Multiple frequency acoustic propagation through clusters of bubbles

Abstract

A numerical study has been conducted in order to examine the effect of bubble clustering on acoustic propagation through bubble clouds. Commonly used effective medium theories make the assumption that the positions of bubbles are statistically independent from each other. It is plausible, however, that there are some scenarios in which this assumption does not apply. For example, bubbles may become preferentially concentrated or clustered as they cross fluid flow streamlines due to their density difference from that of the surrounding liquid. In order to help understand the acoustic implications of bubble clustering, propagation through two types of bubble clouds was investigated numerically. In the first type of bubble cloud the positions of the bubbles were statistically independent from each other. In the second type the bubbles were clustered. Both the average attenuation and the variance in the acoustic pressure amplitude were recorded at nine different frequencies for each type of bubble cloud. It was found that clustering has the effect of reducing the average attenuation from that observed in the nonclustered bubble cloud while increasing the variance. This contrasting behavior suggests a method for detecting the presence of bubble clustering using multiple frequency acoustic propagation measurements.