Numerical experiments on using incline collar rings for controlling mean and fluctuating forces on circular bridge piers

Abstract

This study was done to investigate the effects of angle and spacing of Collar-rings (innovative attachments for scour reduction over the circular piers) on the flow-induced forces on the circular piers. To this end, three angles (0°, 15°and 30°) and three relatives spacing (2/3, 3/3, and 4/3 of pier diameter) for the Collar-rings, have been considered. The ratio of the Collar-rings thickness to pier diameter was considered as 0.15. To compare the Collar-rings and helical cable performance, a circular pier with helical cable (the angle of 15°and the cable–pier diameter ratio of 0.15, suggested by previous experiments) is also numerically simulated. Reynolds number of the flow around circular piers with Collar-rings and helical cable is set to be 9554. In comparison to a plain surface pier, the results show that Collar-rings with the relative spacing of 4/3 for each three desired angles (0°, 15°and 30°) can reduce the mean and fluctuation of pressure, drag and lift coefficients around circular piers. Among tested configurations of the Collar-rings, Collar-rings with the relative spacing of 4/3 and angle of 15°are the best configuration to reduce the flow forces (mean pressure 5%, pressure fluctuation 24%, mean drag 2%, drag fluctuation 55%, fluctuation of lift 19%) around the simulated circular pier. Nevertheless, the helical cable increases flow forces (mean pressure 12%, pressure fluctuation 34%, mean drag 22%, drag fluctuation 110%, fluctuation of lift 30%). In addition to the flow forces and scour control around the circular piers, this tool can be readily and economically installed on the existing circular piers.