Author(s): A. J. S. Cuthbertson; D. A. Ervine
Linked Author(s): Alan J S Cuthbertson
Keywords: Fine sediment; Settling behaviour; Large-scale vortical structures
Abstract: The suspended transport of fine sediment particles in turbulent flows depends on the interaction between the particles and the coherent turbulent structures present within the flow. To study this interaction, the authors conducted a series of visualisation experiments in a transparent-walled flume facility observing the typical settling behaviour of fine sand particles (150-500 microns) within a turbulent open channel flow over a rough gravel bed. The structure of the flow was found to be dominated by large-scale vortical structures, which were shed from the near-bed region of flow. Sediment particle interaction with these vortex structures, which was dependent on particle size, typically led to particle accumulation and an enhanced settling motion of the particles on the downside of the vortices, transferring the particles from the high-speed outer flow to the near-bed low-speed flow. These characteristics of particle trajectory were also demonstrated with a simple Rankine vortex model.