Experimental Investigation of Turbulent Effect on Settling Velocity of Inertial Particles*

Experiments were conducted to investigate the effect of turbulence on the settling velocity increase. First, the settling velocity of particles and the ambient turbulence in the open-channel flow were measured. Second, to identify the influence of advection caused by mean vertical velocity on the settling velocity, experiments using Vertical Recirculating Tube (VeRT) were conducted. In both experiments, the velocity of inertial particles was measured using PTV methods, and turbulence was measured using PIV and LDA. For the last experiment, the settling behavior of inertial particles in turbulent flow was numerically simulated based on the equation of motion for a particle in a fluid flow. The experimental results showed that the settling velocity of particles was faster in turbulent flow than in stagnant water, consistent with the previous studies, and its increase rate depends on the Stokes number, St, which is the ratio of particle relaxation time, τ_p, to Kolmogorov time scale, τ_k. These results may help understand the settling behavior of particles in a natural flow and improve the performance of existing particle tracking models, in which the vertical displacement of a particle was predicted based on the settling velocity in stagnant water.