Numerical study on acoustic release characters of an oscillating bubble in a sound field

Complex nonlinear interactions exist between oscillating bubbles and sound waves. Understanding the modulation mechanism of sound waves on bubble oscillation noise is crucial for acoustic detection and noise control in equipment. The direct numerical simulations approach is used to study the coupling of the oscillating bubble to the acoustic field, and the bubble release acoustic pressure is calculated by the Ffowcs Williams–Hawkings equation. The results reveal that the input sound waves can amplify bubble oscillation, reduce the oscillation period, and induce non-spherical deformation. Further analysis revealed the acoustic characteristics of the bubble oscillation under various conditions. There is a cutoff frequency, which makes the bubble release acoustic pressure amplitude follow a two-stage pattern: an initial increase followed by an exponential decay. And there is a frequency threshold beyond which the bubble release acoustic pressure remains stable. When the input sound wave frequency f is held constant, the acoustic release from the bubble increases linearly with increasing pa, and the maximum bubble acoustic release rate k is approximately 46.7. However, when the fixed f value exceeds the frequency threshold, the bubble's acoustic pressure no longer varies significantly with increasing pa, and the value of k remains stable. Altering the bubble's initial oscillation conditions demonstrates that the sound wave primarily governs the frequency response trend of its oscillatory acoustic pressure, while the frequency threshold is affected by the initial oscillation conditions.