Cavitation bubble collapse near a wall: a numerical study on a bubble initially generated by laser

Cavitation bubble collapse near a wall is investigated by employing a recently developed laser–fluid computational framework to simulate the complete lifecycle of a wall-detached laser-induced bubble, including the water breakdown phase. The model couples compressible multiphase Euler equations, a radiative transport equation and a latent heat reservoir formulation for phase transition. A wide range of nine stand-off ratios gamma element of left bracket 0.79 comma 2.14 right bracket γ ∈ [ 0.79 , 2.14 ] γ ∈ [0.79,\ 2.14] is investigated and directly compared with recent experimental measurements. The simulations reproduce the interfacial dynamics of bubbles with excellent accuracy. Moreover, the computations are capable of reidentifying the three experimentally observed collapse regimes, i.e. purely torus, mixed tip-and-torus and purely tip collapse, and correctly identify the collapse as the dominant source of the peak wall pressure rather than jet impact. A sensitivity analysis shows that only the mixed tip-and-torus regime exhibits strong dependence on the laser absorption coefficient. The simulations give access to the details on pressure, density, temperature and velocity fields inside the bubble and demonstrate that the vapour remains in average thermodynamic equilibrium during most of lifetime. The results reveal significantly different time scales between thermodynamic fields where the gas pressure becomes quasi-uniform inside the bubble during expansion and collapse, whereas the temperature remains strongly non-uniform with persistent spatial gradients. This study provides the most complete numerical reproduction to date of experimental laser-induced bubble collapse near a wall, and offers new physical insight into the coupling between bubble–wall interaction, laser-induced thermodynamics and collapse regimes.