Sound-vortex conversion on droplets: A surface curvature oscillation engine for cavitation

Cavitation, a confusing yet essential natural process, remains the target of intensive scientific research. Discovered through propeller cavitation nearly a century ago, initial theories suggest that bubble collapse initiates cavitation. The mechanism of bubble collapse in cavitation remains unclear, especially in modern cavitation scenarios like sonodynamic tumor therapy or aerodynamic noise without natural bubbles. Therefore, a comprehensive visualization-based cavitation mechanism is vital to comprehend and investigate various cavitation phenomena, from historical propeller cavitation to modern in vivo tumor treatment. This study introduces and discusses the direct conversion between two fundamental motions, sound and vortex, and its application as a universal cavitation mechanism to initiate and sustain tailored long-life cavitation from droplets. The results demonstrate a special acoustic phenomenon and its potential technological applications for harnessing sound with customized acoustics cavitation devoid of bubbles.