Experiment of Local Scour Characteristics of Flow Around Bridge Piers with Different Inclination Angles Based on SFM

The flow scour around bridge piers is the result of the interaction among the flow, sediment and the pier. The complex relationship between water and sediment movement around bridge piers is an important cause of bridge water damage. Quantitative analysis of scour topographic characteristics of bridge piers and its interaction with the flow is an important breakthrough in deeply understanding the mechanism of the flow and sediment interaction around bridge piers and its practical engineering application. In this paper, the flow scour experiment around bridge piers of uniform sediment moving bed was carried out with different inclination angles under two kinds of slope conditions, and four model inclination angles of 0°, 5°, 10° and 15° were set along the downstream direction. The PIV (particle image velocimetry) system was employed to measure the two-dimensional flow field around bridge piers, and the SFM (structure from motion) method was used to achieve the three-dimensional reconstruction of scour topography. Based on this, the characteristics of three-dimensional topography structure of bed surface scour and flow field were analyzed, which are used to build up the coupling relationship between the two. The results show that: 1) The SFM method can be applied to reconstruct the three-dimensional structure of scour topography. As the scour experiment reaches its equilibrium stage, the scour depth in front and on both sides of the model is deeper, and the rear is of convex shape, rising to the bed surface along the flow direction. 2) The size, area and volume of the scour hole increase with the increase of the flow intensity, and decrease with the increase of the inclination angle. As the depth of scour hole increases, the cross-sectional area and three-dimensional morphology increase in parabola with opening upward. 3) As the inclination angle of the bridge pier model increases, the disturbance region of the rear streamwise velocity decreases and the influence region on the spanwise velocity increases. 4) As the model inclination angle increases, influence regions of swirling-strength and shear stress decrease. The deep scour hole around bridge piers can be easily formed by the flow shear stress, and the large-scale streamwise vorticity on both sides of the bridge pier extends downstream, which leads to the formation of shallow long grooves on the back two sides of the bridge pier. © 2021, Editorial Department of Advanced Engineering Sciences. All right reserved.