NEARSHORE SEDIMENT TRANSPORT: UNEARTHED BY LARGE EDDY SIMULATION

The thrust of the present work is to determine to what extent state of the art, three-dimensional and time dependent numerical modeling techniques are capable of resolving detailed sediment transport events as observed in the laboratory and field. Our focus is to study sediment transport patterns over vortex ripples and under waves; hence, the time and spatial scales considered are on the order of seconds and meters, respectively, with field scale Reynolds numbers of roughly 500,000. Towards this end, simulations of sediment transport over prototypical vortex ripples and over real bed topography measured in the field have been performed and compared qualitatively and/or quantitatively to laboratory and field investigations. In these simulations, the volume-filtered Navier Stokes equations (for the flow) and an advection diffusion equation (for the sediment concentration) have been solved with a Large Eddy Simulation (LES) code in three dimensions and time on a curvilinear grid. The code is shown to reproduce the well known sediment transport pattern over vortex ripples, of its trapping in the lee spanwise vortex as the flow slows down, and its subsequent ejection into the outer flow as the flow reverses direction. Simulations of a field experiment conducted at Duck, N.C., by Prof. Tim Stanton predicted the sediment concentration profiles to within a factor of 2-3 and also resolved some of the time-dependent near-bottom suspension events quite nicely. This paper presents a brief overview of the methods and results obtained in the simulations.