Turbulent flow structures and scour hole characteristics around circular bridge piers over non-uniform sand bed channels with downward seepage

Bridges play an important role in the transportation of goods and people across rivers. In civil engineering, one of the most important issues is to protect bridge piers from collapse. In fact, their foundation may be threatened by localized scour, as a result of the flow constriction of the cross-sectional area, and the subsequent increase of the flow velocity [1]. Thus, in order to ensure the protection of such structures, it is of a high priority to predict the flow field and sediment transport around the bridge piers. Many researchers have studied the vortice systems around piers, stating that they primarily aect the local scour [2–6]. Melville and Coleman [5] stated that the flow field around a bridge pier is characterized by down-flow, surface roller, and wake vortices, such as the horseshoe vortex, at the base of the pier, and wake vortices behind the pier. According to Melville [2] and Chiew [4], a horseshoe vortex increases the flow velocity near the bed, and the wake vortex carries the eroded bed material downstream. However, the eect of the pier on flow separation, and the consequent sediment transport, depends on turbulence. Some studies have investigated the stochastics nature of turbulent flow around a pier [2,7–11], but there still remains a lack information concerning the trend of higher order moments for the fluctuating velocities.