Acoustic-induced drag on a bubble

Abstract

This work reports experiments that show that the drag on a bubble can be modified by the presence of isotropic, homogeneous broadband acoustic noise, when the band overlaps the bubble's resonance width. This constitutes an acoustic analog to the Einstein-Hopf drag on an electromagnetic dipole oscillator in the presence of isotropic and homogeneous electromagnetic fluctuations. In contrast with the electromagnetic Einstein-Hopf drag, band- limited acoustic noise can reduce the drag when the lower frequency of the spectrum coincides with the resonant frequency of the bubble. The modification of the drag experienced by a bubble in the presence of acoustic noise suggests possible applications to bubble migration and to heat transfer in a two-phase fluid. Depending on its size (i.e., resonant frequency), a bubble will experience less or more drag when the fluid is insonified with broadband noise, thereby modifying and possibly controlling bubble migration and heat transfer.