Highly-Resolved Large-Eddy Simulation of Sediment Concentration Patterns over a Wavy Bed in the Presence of a Current

Among many sediment transport phenomena, coherent structures, bursts and sweeps have been identified as important mechanisms for entraining sediment into the flow near the bed. Large eddy simulation allows the reproduction of unsteady, intermittent and spatially non-uniform fluid motions and sediment concentration fields. This paper has two main foci: (1) to illustrate that these flow structures and their resultant sediment transport patterns are strongly influenced by the bottom geometry and (2) to illustrate that this coupling between bottom geometry and fluid motion may not be dependent on scale. A comparison is drawn between the transport over straight-crested and three-dimensional ripple geometries at laboratory scale and it is found that although similar structures are responsible for suspension of sediment over the two boundaries, incipient suspension of sediment is confined to regions between lines of zero streamwise curvature over the three-dimensional ripples whereas this effect is absent over the straight-crested ripples. Field-scale flow (Re ~660,000) is solved for over straight-crested ripples to investigate the influence of scale on the flow and similar coherent structures are observed. Future work will implement sediment transport in this field-scale flow.