Experimental study of underwater explosions below a free surface: Bubble dynamics and pressure wave emission

The current work experimentally studies the complex interaction between underwater explosion (UNDEX) bubbles and a free surface. We aim to reveal the dependence of the associated physics on the key factor, namely, the dimensionless detonation depth γ (scaled by the maximum equivalent bubble radius). Four typical bubble behavior patterns are identified with the respective range of γ: (i) bubble bursting at the free surface, (ii) bubble jetting downward, (iii) neutral collapse of the bubble, and (iv) quasi-free-field motion. By comparison of the jet direction and the migration of the bubble centroid, a critical value of γ is vital for ignoring the effects of the free surface on UNDEX bubbles. Good agreements are obtained between the experimental data and Zhang equation [Zhang et al., “A unified theory for bubble dynamics,” Phys. Fluids 35, 033323 (2023)]. Additionally, the dependence of the pressure signals in the flow field on γ is investigated. The peak pressure, impulse, and energy dissipation in the UNDEX are investigated.