Near-field characteristics of particle-driven plumes induced by near-wall jet

Particle-driven plumes induced by near-wall jet are common in engineering, such as deep-sea mining and dredging projects. Due to the difficulty of identifying the flow containing high concentrations of sediment particles with conventional measurement techniques, this study introduces digital image processing (DIP) techniques, aiming to comprehensively analyze the near-field characteristics of the particle-driven plumes for five different jet parameters through physical experiments. The results indicate that DIP technology can clearly identify the plume edges, and the plume motion is affected by the combination of particle inertia, buoyancy accumulation due to density gradient, environmental entrainment, and wall confinement. The near-field dimensionless plume fronts are power-law dependent on time, and the diffusion rate of the downstream plume decreases rapidly within 2 s after the near-wall impingement. Small jet angles and large jet velocities enhance horizontal diffusion kinetic energy, and long jetting duration increases buoyancy accumulation, both leading to further plume fronts. The dimensionless plume average heights are more sensitive to jet velocities and jetting duration. This research proposes horizontal diffusion index Ih and vertical structural index Iv for plume classification, which declined in a linear and power-law pattern after 20 s, respectively. During the diffusion process, high-concentration structures within the plume consistently account for a small proportion, while low and medium concentration structures increase linearly with time. The findings in the influence of jet parameters on the dimensionless characteristics of plumes, and the mechanism of plume evolution induced by near-wall jet, are helpful for reducing the environmental disturbance caused by deep-sea mining.