Motion of a Free-Settling Spherical Particle Driven by a Laser-Induced Bubble

We document experimentally four different interactions of a laser-induced bubble and a free-settling particle, with different combinations of the geometric and physical parameters of the system. Our force balance model shows that four nondimensional factors involving the particle radius a, the maximum bubble radius Rmax, the initial separation distance l0 between the particle center and the bubble center, the fluid viscosity μf, and the particle and fluid densities ρp and ρf, respectively, in detail l0/Rmax, a/Rmax, ρp/ρf, and μ∗=μfTc/ρfRmax2, where Tc=0.915Rmaxρf/(p-pv), influence the particle-bubble dynamics, and reasonably predict the maximum particle velocity and the limiting condition when the particle starts to "bounce off" the bubble during bubble growth. In particular, we also discover the high-speed ejection of the particle, and a cavity behind the particle, in cases when initially the particle is in very close proximity to the bubble. These observations offer new insights into the causal mechanism for the enhanced cavitation erosion in silt-laden water.