CFD ANALYSIS OF BRIDGE PIER GEOMETRY ON LOCAL SCOUR POTENTIAL

Abstract

Scour at bridge piers is one of the highest contributing failure factors of bridges. One way to minimize local scour is to alter the flow around a bridge pier and thereby reduce the strength of the downflow and horseshoe vortices. There are many flow-altering scour countermeasures including altering the geometry of the pier itself or by adding a plate or sheath to the base of the pier. Computational Fluid Dynamics (CFD) is a useful method to model and analyze the effects of pier configuration on flow velocity distribution profiles and bed shear stress. The hydrodynamic component of local scour at a circular pier is modeled by solving the Reynolds- Averaged Navier–Stokes (RANS) equations with k–ω and k-ε turbulence closure models. The realizable k-ε model most closely predicted the velocity components for a cylinder in steady flow obtained experimentally in literature. This model was then used to predict velocity distribution profiles and bed shear stress for a Reynolds number of 1.7 × 105 for the following circular pier attachments: tapered streamlined sheath, delta vane, guide wall with slanting plates, and angled plate footings. The reduction in simulated maximum bed shear stress compared to the circular pier was 30% for the delta vane and angled plate footings, 20% for the tapered streamlined sheath and 15% for the guide wall with slanting plates. The delta vane was then compared to the circular pier for a Reynolds number of 5.1 × 106. The reduction in maximum bed shear stress was 22%. By reducing bed shear stress, these pier configurations demonstrate the ability to alter the flow near the pier and reduce the scour potential.