Investigation of the energy conversion process of a single bubble collapsing near different boundaries

The objective of this paper is to investigate the energy conversion process of a single bubble collapse under different boundaries using combined experimental and computational modeling. In the experiments, high-speed photography is used to record the temporal and spatial evolution of a single bubble collapse near free-field, rigid, and elastic boundaries. The different energies of bubbles in the initial standoff distance range from γ = 0.8 to 1.7 are calculated based on the experimental data. This paper compares the energy conversion process of near-spherical bubbles near the elastic and rigid boundaries when γ = 1.4. In the numerical simulations, a 3D weakly compressible model is introduced to predict the transient process of the single bubble dynamic patterns and its surrounding flow structure. The results show that boundaries have an inhibitory effect on the conversion of potential energy into kinetic energy. When a bubble collapses near a boundary surface, the energy conversion ratio, defined as the dimensionless parameter η_kin/pot (the ratio of the potential energy over the maximum kinetic energy), is always smaller than that in the free field. The η_kin/pot of the elastic boundaries is larger than that of the rigid boundary when γ = 1.4. This is due to the fact that boundaries affect the propagation of pressure waves, the dynamic behaviors of the bubble change, and the transformation process of different energies is influenced. The difference can be explained by the η_kin/pot of experimental and numerical methods. Based on the above analysis, we propose a theoretical framework for the energy conversion process during bubble collapse near different boundaries.