Large-Eddy Simulation of Wave-breaking Induced Turbulent Coherent Structures and Suspended Sediment Transport on a Barred Beach

To better understand the interaction between wave-breaking induced turbulent coherent structures and suspended sediment transport, we report a 3-D Large-Eddy Simulation (LES) study of wave-breaking over a near-prototype scale barred beach. The numerical model is implemented using the open-source CFD toolbox, OpenFOAM®. The numerical model is validated with measured free surface elevation, turbulence averaged flow velocity, turbulent kinetic energy, and for the first time, the intermittency of breaking wave turbulence on the bar crest. Simulation results confirm that as the obliquely descending eddies (ODEs) approach the bed, significant bottom shear stress is generated. Remarkably, the collapse of ODEs onto the bed also causes drastic spatial and temporal changes of dynamic pressure which may encourage momentary bed failure and a reduction of bed shear strength via upward-directed pore pressure gradient. By allowing sediment to be suspended from the bar crest, intermittent high sediment suspension events and their correlation with high turbulence and/or high bottom shear stress events are investigated. The simulated intermittency of sediment suspension is similar to previous field and large wave flume observations. Model results suggest that high sediment suspension events near the bottom (2% of the local water depth) is mainly controlled by bottom shear stress, while moving further away from the bottom (23% of the local water depth), sediment suspension becomes more affected by breaking wave turbulence.