Investigation of the flow behaviour and local scour around single square-shaped cylinders at different positions in live-bed

Abstract

Scour around non-circular cylinders has seldom been studied before. This paper aims to numerically investigate the flow behaviour and evolution of local scour around two single square-shaped piers with 90° (square pier) and 45° (diamond pier) orientation angles to the flow under steady-current and live-bed conditions. For this purpose, a coupled approach between a hydrodynamic and a morphodynamic model is developed and validated against flow and scour experimental data sets. Hydrodynamic model simulations reveal the formation of strong horseshoe vortices (HSVs) upstream of the square pier compared to the diamond pier. The scour simulation results show a faster rate of increase in the scour depth around the square pier, which leads to a deeper equilibrium scour hole. The model gives values of normalized quasi-equilibrium scour depths of Seq/wp = 1.94 and 1.00 for the square and diamond piers, respectively, where Seq is the quasi-equilibrium scour depth, and wp is the pier's projected width under steady current flow and live-bed conditions. It is discovered that the impact of other factors, such as bed material gradation, Froude number, Shields Parameter, as well as flow depth, can be as important as the shape factor in the study of equilibrium scour depth in live-bed conditions.