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CFD modeling of tidal bores: development and validation challenges

ABSTRACT A tidal bore is a natural estuarine phenomenon forming a positive surge in a funnel-shaped river mouth during the early flood tide under spring tide conditions and low freshwater levels. The bore passage may induce some enhanced turbulent mixing, with upstream advection of suspended material. Herein, the flow field and turbulence characteristics of tidal bores were measured using both numerical computational fluid dynamics (CFD) and physical modeling. This joint modeling approach, combined with some theoretical knowledge, led to some new understanding of turbulent velocity field, turbulent mixing process, Reynolds stress tensor, and tidal bore hydrodynamics. Thétis is a CFD model using the volume of fluid technique to model the free-surface and Large Eddy Simulation (LES) technique for the turbulence modeling. Physical data sets were used to map the velocity and pressure field and resolve some unusual feature of the unsteady flow motion. A discussion will be provided to explain why a detailed validation process, involving a physical knowledge of the flow, is crucial. Comparison of the numerical model results and experimental data over broad ranges of conditions for the same flow is mandatory. The validation process from two-dimensional to three-dimensional will be commented and difficulties will be highlighted.