Linear stability analysis for bubble shape of acoustic cavitation with different ultrasonic frequencies

In the present study, the bubble shape stability of acoustic cavitation is numerically investigated with different ultrasonic frequencies by solving the Keller equation and dynamic equation of distortion amplitude simultaneously to investigate the effect of ultrasonic frequency on the stability. The bubble shape is distorted at higher pressure amplitude and larger bubble size, and the lower degree of spherical harmonics contributes to the instabilities. The stable zone in a stability diagram of parametric instability is similar to that of afterbounce instability at small ultrasonic frequency (similar to 20 kHz), although the parametric instability becomes the main factor to cause bubble shape instability at higher ultrasonic frequency (f > 40 kHz) because the afterbounce instability becomes difficult to occur due to the short time period from Rayleigh collapse to the start moment of the next ultrasonic cycle. Moreover, the slope of the main stable and unstable boundaries in a phase diagram between pressure amplitude and bubble radius becomes smaller with ultrasonic frequency suggesting that the width of bubble equilibrium size distribution becomes narrower at higher ultrasonic frequency.