Large-eddy simulation of sediment transport: Currents over ripples

A large-eddy simulation has been performed to study the detailed sediment dynamics that occur in channel flow over ripples. The code solves the Navier-Stokes equations and an advection-diffusion equation for the sediment, and has been verified to produce quantitatively accurate hydrodynamic results for the flow domains used in this study. The main features of interest in this how are seen because of the high resolution of the grid, especially near the ripple boundary. This yields a detailed bottom shear stress distribution, properly identified coherent structures, and resolved sharp gradients in the sediment concentration. Globally, the sediment is carried up into the flow from locations where the shear stress is high-on the upslopes of ripple crests-and is advected downstream by the current and upward by the vertical velocity component. Regions of positive vertical velocity are associated with Gortler vortices, which represent a significant sediment transport mechanism in this flow.