Interaction between horseshoe vortex structure and sediment transport around a river rectangular pier using a solid-liquid two-phase turbulent LES model

Abstract

Most river bridges are endangered by local scour upstream of bridge piers as a result of large floods. Local scouring is primarily caused by a three-dimensional horseshoe vortex (3D-HV) forming around the upstream face of the pier. Numerical simulations of local scour around a pier are mostly conducted using a fixed-bed even though the interactions between suspended sediment and HV structures (one of the factors influencing 3D-HV structures around piers) may be important. This study aims to clarify how the presence of suspended sediment affects the 3D-HV structure around a rectangular pier. We apply movable-bed analysis using a multiphase turbulent LES model (grid-averaged Lagrangian-LES model) to conduct a local scour numerical experiment around a rectangular pier. Furthermore, movable-bed and fixed-bed results are compared. The maximum scour depth in the simulation is found to be close to the value (RMS value equal to 9 %) determined experimentally. The 3D-HV structures are found to be quite different in the movable-bed and fixed-bed simulations. In particular, the HV is generally weaker in the movable-bed simulation compared to the fixed-bed simulation. The torque produced by the drag force between particles and fluid phases generated by the suspended sediment is significantly deformed, changing the 3D-HV structure.