Quantitative analysis of surface mode oscillations of acoustically excited microbubbles

This study investigates the non-spherical dynamics in acoustically driven microbubbles using two modeling approaches: a Reduced-Order Model (ROM) and Direct Numerical Simulations (DNS) performed with the ALPACA multiphase flow solver. The ROM couples the radial dynamics, described by the Keller-Miksis equation, with axisymmetric surface-mode oscillations, resulting in a computationally efficient framework for describing the non-spherical oscillations of bubbles. The DNS approach directly solves the governing compressible Navier-Stokes equations with interface-capturing making this approach computationally more expensive. Accurate interface-capturing and capillary calculations are critical for surface-mode oscillation in the DNS; thus, two different models are evaluated in this study: a sharp level set method and a diffuse-interface method. The diffuse-interface method demonstrates excellent agreement with the ROM in predicting both the spherical oscillations and stable surface-mode amplitudes, while the level set method tends to overdamp surface perturbations and is thus considered inaccurate for most cases involving non-spherical bubbles. Both the ROM and diffuse-interface--based DNS predict spherical stability and bubble breakup similarly, with bubble breakup occurring when surface-mode amplitudes diverge. These findings show that the ROM can serve as an efficient predictor of bubble breakup, while DNS simulations with the diffuse-interface approach provide detailed insight into the nonlinear dynamics and breakup processes. Together, these methods offer a robust and complementary framework for analyzing non-spherical bubble dynamics in acoustic fields.