Non-spherical oscillations and induced microstreaming of single bubble in standing wave field

The evolution of oscillations in freely suspended microbubbles that are transitioning from spherical to nonspherical shapes in a standing-wave acoustic field was investigated along with the resulting acoustic microstreaming using a combination of experimental methods and numerical simulations. In this study, an ultrasonic levitation system was first employed to induce periodic oscillations in a single bubble located near the center of the acoustic wave field. Subsequently, a high-speed camera was used to capture the oscillatory behavior of the bubble and the trajectories of tracer particles. The trajectories of the tracer particles were then superimposed to generate images of the acoustic microstreaming structures. In addition, numerical simulations based on the Navier-Stokes equations and the Arbitrary Lagrange-Euler (ALE) method with moving grids effectively reproduced dynamic evolution of the interface between the bubble and the surrounding microstreaming field. Furthermore, the effects of driving frequency, bubble radius, and driving pressure on the non-spherical oscillation modes of bubbles and the structure of acoustic microstreaming were investigated. The mechanisms underlying vortex structure formation and the distribution characteristics of shear stress during multimode-coupled bubble oscillations were elucidated. These findings provide valuable insights for the application of acoustic microstreaming in particle manipulation, targeted drug delivery, and related fields.