Non-hydrostatic RANS simulation of nearshore Langmuir circulation and sediment transport

Langmuir turbulence in the coastal ocean is driven by winds and waves and is characterized by Langmuir cells (LCs) that can span the full depth of unstratified water columns in the coastal ocean. LCs consist of wind-aligned parallel counter-rotating vortices, which when spanning the full-depth of the water column can result in significant sediment resuspension and subsequent lateral transport. Non-hydrostatic Reynolds-averaged Navier-Stokes (RANS) simulations of LCs in the surf-shelf transition zone of the coastal ocean will be presented. In this region, the structure of the LCs is dependent on depth-refraction of the gravity surface waves generating the LCs, surface wave breaking, and the alongshore current generated by the wave-breaking. Overall, the present simulations account for effects of nearshore processes on LCs, unlike earlier simulations which have focused on LCs in the open ocean away from coastal boundaries. In addition to LCs, the resolved flow is characterized by a wind-driven, onshore-directed surface shear current and a compesating undertow. Given this neashore circulation, lighter sediments suspended by LCs will be transported onshore and heavier suspened sediments will be transported offshore. This sediment transport behavior will be investigated in terms of various sediment classes characterized by their density and settling velocity.