Abstract
Abstract. Wave-induced boundary layer (BL) flows over sandy rippled bottoms are studied using a numerical model that applies a one-way coupling of a "far-field" inviscid flow model to a "near-field" large eddy simulation (LES) Navier–Stokes (NS) model. The incident inviscid velocity and pressure fields force the LES, in which near-field, wave-induced, turbulent bottom BL flows are simulated. A sediment suspension and transport model is embedded within the coupled flow model. The numerical implementation of the various models has been reported elsewhere, where we showed that the LES was able to accurately simulate both mean flow and turbulent statistics for oscillatory BL flows over a flat, rough bed. Here we show that the model accurately predicts the mean velocity fields and suspended sediment concentration for oscillatory flows over full-scale vortex ripples. Tests show that surface roughness has a significant effect on the results. Beyond increasing our insight into wave-induced oscillatory bottom BL physics, sophisticated coupled models of sediment transport such as that presented have the potential to make quantitative predictions of sediment transport and erosion/accretion around partly buried objects in the bottom, which is important for a vast array of bottom deployed instrumentation and other practical ocean engineering problems.
Highlights
Rippled seabeds frequently occur in coastal waters with sandy bottom, and the geometry of such ripples strongly affects wave-induced bottom boundary layer (BL) processes
A new hybrid Large Eddy Simulation (LES) approach for modeling the Navier–Stokes equations was applied to the simulation of wave-induced sediment transport over sand ripples
Harris and Grilli (2012) have already shown this approach to be accurate for modeling turbulent oscillatory boundary layers over flat beds, and practical for coupling the LES model to numerical wave tanks
Summary
Rippled seabeds frequently occur in coastal waters with sandy bottom, and the geometry of such ripples strongly affects wave-induced bottom boundary layer (BL) processes. For modeling experiments of oscillatory BLs inside laboratory water tunnels, the assumption of periodic boundary conditions may be suitable for the near-field perturbation flow, as long as turbulence is sufficiently well resolved This simplification permits simulations over even smaller domains of simple shape, which adequately represent flow conditions in much larger experimental setups. Note that completely independent developments of the LES model of Cui and Street (2001), other than those that led to the work of Gilbert et al (2007) and to the present work on suspended sediment transport, were pursued by Zedler and Street (2001, 2006) and, to study bedform evolution, by Chou and Fringer (2008, 2009, 2010) The latter authors extended the model to consider an evolving bed, and, by devoting sufficient computer power and time, they were able to directly simulate the formation of vortex ripples on a sandy bed rather than assuming an initial perturbed shape as will be done here.
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