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 $\gamma$ and size ratio $\eta$ 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, $V_0=1.1 p_0R_0/(\rho cR_l)((\gamma (1+\eta )-1)/\eta )^{-1.6}$ for the shock-driven stage and $V_m={}(1+(0.8-0.5\gamma )\eta ^{0.75})V_0$ for the flow focusing stage in the strong jet regime, both of which agree closely with experimental and numerical measurements. Here, $V_0$ and $V_m$ denote the velocity increments associated with shock-wave-induced acceleration and flow focusing stages, respectively. The variables $p_0$ , $R_0$ , $\rho$ , $c$ and $R_l$ 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 $(\eta ,\gamma )$ phase diagram delineates the weak, strong and explosive jets, with regime boundaries accurately captured by the theoretically derived transitions.