Calculations of Nonsubmerged Groin Flow in a Shallow Open Channel by Large-Eddy Simulation

Rigid structures, such as groins or spur dikes, are constructed along riverbanks for various purposes, which pose computational challenges for unsteady flow in engineering mechanics. This paper presents a study of turbulent flow past a series of groins in a shallow, open channel by large-eddy simulation (LES). A direct-forcing immersed boundary method (IBM) was implemented to approximate complex boundaries around groins with round heads. The time-averaged velocities and turbulence intensities at the water surface obtained by an experiment using particle image velocimetry (PIV) were employed to validate the LES model, finding a satisfactory agreement between laboratory data and model results. Subsequently, the numerical model was employed to investigate the impact of groin parameters (i.e., head shape, aspect ratio L/D, and length L) on the flow properties. Model results showed that a rectangular-headed groin generates higher turbulence intensities and larger vortices than a round-headed groin. On the other hand, the groin aspect ratio (L/D) affects the strength of turbulence intensities, vorticity in the mixing layer, and flow patterns in the groin field. Consistent with previous studies, the groin length (L) significantly affected the turbulent intensities and the vorticity but had little influence on the streamline in the recirculation zone. Eddies were produced at the groin tips and transported downstream. The shape of the vortex group varied as the vortices were transported downstream by the flow. Coherent structures were visualized by Q-criterion around the groin tips.