Retardation of settling velocity in sinusoidally oscillating flows--settling velocity of floc in Turbulent flows (I)-

摘要

The densities of kaolin floc have been obtained as a function of floc diameter by measuring the terminal settling velocities of gravitational fall for stationary fluid. The trajectories and terminal settling velocities of kaolin floc in sinusoidally oscillating fluids, were then studied by obtaining numerical solutions to the nonlinear Lagrangian momentum equation with a particle-fluid drag which is a function of the particle Reynolds number. The terminal settling velocities obtained numerically for vertical and horizontal oscillating flows, were found to be lower than those for stationary fluid. The retardation of the settling velocity occurred for fd_0 >0.1cm/s, where f is the frequency of the oscillating flow and d_0 is the diameter of floc. This retardation was primarily attributed to the increase of phase lag and the decrease of amplitude of floc oscillation, with appreciable secondary influences arising from the increase in the turbulence intensity, the diameter of floc, and the frequency of oscillating flow. It was concluded that the mechanism of this retardation obtained for terminal settling velocities of kaolin floc, in sinusoidally oscillating fluids, was similar to the results obtained for sand particles in other studies previously presented.