A Large-Eddy Simulation Study on the Flow Structure of a Solitary Wave Breaking in the Inner-Surf and Swash Zones

Several recent post-tsunami surveys have found that a significant amount of soil erosion and foundation failure seem to occur during the drawdown stage of the tsunami impact. In this study, 3D Large-eddy simulations were carried out to investigate the flow structure of a solitary wave breaking in the inner-surf and swash zones and their implication to sediment transport. The numerical model, implemented using OpenFOAM, solves the filtered Navier-Stokes equations for two immiscible fluids (air and water phases) using a volume of fluid method. Flows propagating on a smooth planar beach were modeled using near-wall modeling. The numerical model was validated with the laboratory wave flume experiment reported by Sumer et al. (2011, J. Geophys. Res.: Oceans). The size of the model domain was identical to the physical experiment, and the model domain was discretized using an unstructured mesh refined from a general grid size of O(10 mm) to that of O(1 mm) near the bed. Model results show that free-surface elevation is predicted very well (index of agreement larger than 0.95). The predicted bottom shear stresses from different near-wall modeling treatments are evaluated using measured data. Modeled results suggest that the bottom shear stress is strongly affected by turbulent coherent structures. A hydraulic jump forms where backwash flow impinging back to the inner-surf zone, which further generates complex turbulence coherent structures (i.e., vortex turning) and strong turbulence production. The flow separation, identified by the local strong adverse pressure gradient and vorticity criterion, is also observed under the hydraulic jump. The vertical flow formed due to the flow separation carries a high level of turbulent kinetic energy further offshore. The relation among the flow separation, turbulent coherent structures, and turbulent kinetic energy budget is further analyzed. More detailed discussion on the fate of turbulence and implication to sediment transport will be presented at the conference.