Dynamics and jetting behaviors of horizontally distributed out-of-phase double bubbles near a free surface

The dynamics of bubbles near a free surface are of significant importance in marine engineering. In this study, we investigate the nonlinear evolution of two horizontally arranged, out-of-phase bubbles located near a free surface. Numerical simulations in this study are based on a three-dimensional Eulerian finite-element method. This approach is combined with adaptive mesh refinement technology to accurately capture the behavior of compressible inviscid fluids. First, the accuracy and convergence of the numerical model are validated through a comparison with the experimental data. Subsequently, the influence of varying phase differences and distances from the free surface on the coupling characteristics during bubble pulsation, migration, and collapse is systematically analyzed. The results demonstrate that the combined effects of the free-surface reflection and pressure wave interference between out-of-phase bubbles accelerate the collapse process, leading to distinct patterns in lateral migration and free surface spike evolution. Furthermore, four characteristic jet impingement modes are identified. The distribution of jet velocities across various conditions is examined, and the underlying mechanisms of jet enhancement are discussed. This work provides useful additional insight into bubble-free-surface interactions.