Characterization of the intermittent behavior of sediment transport from numerical simulations on a flat bed channel

Abstract:

The bedload transport of sediment particles is strongly determined by coherent structures of the near bed flow. Many experimental and computational studies have shown this interaction, but the mechanisms that control some important phenomena such as the initiation of particle movement, the probability distribution of resting time and the intermittency in particle transport are not yet fully understood. In order to give new insights into these processes, we carried out simulations over a flat bed channel. We used CFD (Computational Fluid Dynamics) to solve the 3D Navier-Stokes equations for the flow in a high resolution grid and DEM (Discrete Element Method) to solve the particle dynamics (LIGGGHTS, http://www.cfdem.com/liggghts) using a two-way coupling approach. The objectives are to elucidate i) how the forces determine the intermittency in the sediment transport, and ii) how relevant are collisions between particles during this process. We show that the drag force, generated by the turbulent coherent structures near the bed, is the main driving force in the intermittent jumps of the particles. We conclude that the probability distribution of the resting time of the particles is a key variable that could explain the intermittency in the transport. Therefore, computing the interaction between particles may modify the shape of the probability distribution functions.