Modeling instantaneous discharge of unsorted particle cloud in ambient water by an Eulerian-Lagrangian method

The mixing characteristics of waste particles (e.g. dredged sediments) of variable size discharged into ambient water is studied numerically by an Eulerian-Lagrangian method. A three-dimensional (3D) numerical model using the modified k-ε parameterization of turbulence for the fluid phase (water) and a Lagrangian method for the solid phase (particles) has been developed. In the model the wake turbulence induced by particles has been included as additional source and sink terms in the k-ε model; and the variable drift velocities of the particles are treated efficiently by the Lagrangian method in which the particles are tracked explicitly and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumping a cloud of particles is governed by the total buoyancy of the cloud, and the drag force on each particle. The computed results show a roughly linear relationship between the displacement of the frontal position and the longitudinal width of the particle cloud. Radial vortices appear before the particles reach the bottom. The particle size distribution in the cloud affects the rate of increase of the cloud size, as well as the rate of change of frontal position. The largest particles in the cloud dominate the flow behavior. The computed results are compared with the results of laboratory experiments and satisfactory agreement is obtained.