Abstract
This research explores how a circular collar with a tilt angle (counterclockwise around the direction of the channel cross-section) could affect the local scour depth around a single cylindrical pier in clear-water based on Large Eddy Simulation (LES) in six cases. The results show that a horizontal circular collar is the best for reducing the local scour depth. With the increases of the tilt angle, the effect on reducing the local scour depth decreases gradually and is even counterproductive at the scour equilibrium. At the early stage of scouring, cases with circular collars show obvious scouring depth reductions. The smaller the tilt angle is, the better and longer-lasting the protection that the circular collar can provide. When the tilt angle is smaller than 5°, the location of the maximum local scouring is around 90–115° (the angle is measured clockwise from the flow direction) on both sides of the pier. When the tilt angle is greater than 5°, the depth of local scouring in the range around −115° to 115° is close to the maximum local scouring depth. Significantly larger areas reach the maximum scouring depth when the tilt angle increases. Compared to Case 1 (the pier without a circular collar), in the cases with a circular collar, the topographies downwards the pier in 1.0D (D is the diameter of the bridge pier) are changed to siltation from scouring. The topography downwards the pier changes from scouring to siltation with the increase of the tilt angle, and the shape of siltation changes from a long-narrow rectangle to an equilateral triangle. This study may provide valuable insights into the protection of the local scour of the pier.
Highlights
Local scour is a natural phenomenon and usually occurs near obstructions such as piers and abutments
The results showed that the dominant feature of the flow near a pier is a large-scale eddy structure or the system of vortices developed by the pier and these vortex systems are the basic mechanism of local scour
Chen et al [14] studied the local scour depth of a cylindrical pier with a hooked collar at two different locations, and the results indicated that the collar at the bed level is more effective
Summary
Local scour is a natural phenomenon and usually occurs near obstructions such as piers and abutments. Studied the local scour depth of a cylindrical pier with rectangular collar and circular collar by experiment and simulation, and the results indicated that the rectangular collar is more effective. The circular collars in different cases are rotated counterclockwise in different angles around the direction of the channel cross-section in clear-water using the Large Eddy Simulation (LES) model, which has proven to be competent for the simulation of local scour. The numerical modeling and setup, including the introduction of LES, the verification of the method used in this study, the model and parameters studied in this paper; the results and discussion, including the characteristics of the local scour depth and the topography around the pier in each case and the characteristics and mechanism of the effects of the circular collar with tilt angles on local scour depth around a single cylindrical pier
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