Jet formation in air bubbles induced by cavitation bubbles

Bubble pairs are effective modulators of liquid jets. We investigate the jetting of an air bubble driven by a laser-induced cavitation bubble using high-speed imaging, compressible volume-of-fluid (VoF) simulations and theoretical analysis. Three distinct jet types emerge, depending on the stand-off distance γ and size ratio η between the bubbles. Jet formation proceeds through two stages: an initial shock-induced acceleration followed by flow focusing on the concave liquid–air interface. We derive scaling relations, V₀=1.1 p₀R₀/(ρ cRₗ)((γ (1+η )-1)/η )-1.6 for the shock-driven stage and Vₘ=(1+(0.8-0.5γ )η 0.75)V₀ for the flow focusing stage in the strong jet regime, both of which agree closely with experimental and numerical measurements. Here, V₀ and Vₘ denote the velocity increments associated with shock-wave-induced acceleration and flow focusing stages, respectively. The variables p₀ , R₀ , ρ , c and Rₗ represent the initial pressure and radius of the cavitation bubble, the fluid density, the speed of sound in the liquid and the maximum volume-equivalent radius of the cavitation bubble, respectively. A (η ,γ ) phase diagram delineates the weak, strong and explosive jets, with regime boundaries accurately captured by the theoretically derived transitions.