Dynamics of ultrasound-induced cavitation bubbles in non-Newtonian liquids and near a rigid boundary

The dynamics of ultrasound-induced cavitation bubbles situated in non-Newtonian liquids and near a rigid boundary are investigated experimentally by acoustic measurements and high-speed photography with up to 4 million frames/s. The non-Newtonian liquids consist of a 0.5% polyacrylamide (PAM) aqueous solution with a strong elastic component and a 0.5% carboxymethylcellulose aqueous solution with a weak elastic component. The maximum velocity of the re-entrant liquid jet and the pressure amplitude of the acoustic transients emitted during first bubble collapse are diminished by the polymer additives. The most significant reduction was found in the elastic PAM solution. It might be caused by an increased resistance to extensional flow which is conferred upon the liquid by the polymer additive. The results are discussed with respect to the mechanisms of cavitation erosion of rigid materials. The material presented may also be useful for comparison with future numerical work.