Seminar: "Numerical Modelling of Flow Structures and Sediment Behaviors Behind Hydraulic Structures" (Van Thinh Nguyen)

Speaker: Van Thinh Nguyen, Department of Civil and Environmental Engineering, Seoul National University, South Korea

Abstract:  In this study, a combined numerical technique of large eddy simulation (LES) and discrete element method (DEM), based on the open sources package OpenFOAM, is employed to investigate the flow structures and sediment behaviors behind hydraulic structures, including various inclined backward-facing steps (BFSs) and a submerged sluice gate. The LES-DEM coupled model is further expanded to a three-phase model (water-air-sediment) incorporating air phase. The validation of the numerical model shows a good agreement between the simulation results and observed data obtained from different experiments. The simulation results reveal that the near-wall mean streamwise velocity is the most influential factor in determining the bedload transport rate and scour depth downstream of the apron. The bedload transport rate and the maximum scour depth are significantly reduced by the air injection, which also decreases the nearwall mean streamwise velocity. The quadrant analysis for bedload transport is performed, and the results demonstrate that the sweep event plays a significant role in moving most sediment to downstream of the reattachment point. It also reveals that without air injection, the sweep event is primarily responsible for the initial scour process. Keyword: Bedload transport; turbulence structures; LES-DEM coupling; quadrant analysis; three-phase flow.