Large-eddy simulation of sediment transport: Currents over ripples

A large-eddy simulation has been performed to study the detailed sediment d ynamics 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 t his how are seen because of the high resolution of the grid, especially nea r the ripple boundary. This yields a detailed bottom shear stress distribut ion, properly identified coherent structures, and resolved sharp gradients in the sediment concentration. Globally, the sediment is carried up into th e flow from locations where the shear stress is high-on the upslopes of rip ple crests-and is advected downstream by the current and upward by the vert ical velocity component. Regions of positive vertical velocity are associat ed with Gortler vortices, which represent a significant sediment transport mechanism in this flow.