Drift velocity in sediment-laden downward jets

The drift velocity, defined as the velocity of individual phase relative to the water–sediment mixture, is a key variable in two-phase mixture model. In this paper, a relation for the drift velocity in sediment-laden jets, expressed as a power series of the nozzle Stokes number, was derived by using the perturbation approach. It shows that except the gravity and turbulent diffusion, effects of particle inertia, inter-phase interaction, and other forces contained in the first-order particle inertial corrections also play significant roles in sediment-laden jet flows. Based on the relation for the drift velocity, the velocity and concentration distribution were obtained from the similarity solutions for sediment-laden jets. The calculated concentration and velocity profiles agree well with the experimental observations in literature. Furthermore, analysis on the sediment diffusion coefficient shows that the fluid turbulence is not the only driving force for the sediment diffusion in sediment-laden jets; the effect of particle turbulence on the behavior of sediment-laden jets is also significant with the increasing of particle inertia.