Sediment transport by coherent structures in a turbulent open channel flow experiment

Abstract

In order to obtain more insight into the vertical transport of suspended sediment, an experiment was performed using a combination of PIV and PTV for the measurement of the fluid and particle velocity respectively. In this experiment, the particles were fed to the flow at 16 and 75 water depths from the measurement section with an injector located at the centerline of the channel near the free surface. At 16 water depths from the sediment injection, most sediment is still near the free surface, and the sediment is transported downwards in sweeps, thus leading to a mean particle velocity that is faster than the mean fluid velocity. It appears that in this situation, downward going particles are indeed found in sweeps (Q4), whereas upward going particles are preferentially concentrated in both Q1 and Q2 events. In the fully developed situation on the other hand, upward going particles are preferentially concentrated in ejections, while downward going ones are found in both Q3 and Q4 events, with a relatively increased frequency in Q3, and a decreased one in Q4. The increased number of particles in Q2 and Q3, which have low fluid velocities, leads to a mean particle velocity lower than the mean fluid velocity.