Response of sediment cloud dynamics to initial discharge and ambient flow conditions

When the bulk volume of dredged sediments is released into the water within a relatively short time, the sediment cloud exhibits complex diffusion and settling characteristics, which can negatively impact the water quality in the disposal area. In this study, the computational fluid dynamics-discrete element method coupling model and experiments were used to investigate the influence of particle size, inlet cross-sectional geometry, and cross-flow on sediment cloud behavior. The results reveal that the movement characteristics of the sediment cloud are sensitive to particle sizes prior to seafloor impingement, with sustained discharge developing a quasi-steady sediment-laden jet. The cross-sectional geometry of the inlet also significantly affects the plume center velocity, with the influence zone extending approximately ten times the equivalent diameter downstream. Specifically, non-circular inlets (square, triangular) induce flow asymmetry and enhance near-field fluid entrainment, while the coaxial annular inlet exhibits the smallest spread due to the shielding effect of the outer annular flow. The presence of cross-flow promotes lateral spreading. Among the different cross-sectional geometries tested, the coaxial annular inlet demonstrates the optimal cross-flow penetration depth (minimal deflection) due to its protective outer flow. The triangular inlet generates the largest lateral spread by enhancing mixing with the ambient fluid. While the spread of the square inlet is smaller than the triangular inlet, its final diffusion pattern under cross-flow converges toward that of the circular inlet.