Three Dimensional Turbulent Flow Field Research In The Process Of Local Scour Hole Development Around Bridge Piers

Local scour around the bridge pier or abutment is one of the main reasons for bridge damage. Thus, correct prediction of local scour depth and dimensions of scour hole plays an important role in bridge design project and safe operation. The couple calculation of flow and riverbed deformation around bridge piers is a new method in computation hydraulics, however, due to the complexity of flow structure and sediment transport within the scour hole, the present flow-sediment couple model cannot simulate the scour evolution accurately. Therefore, this paper mainly focuses on the change of the flow field around bridge pier during the scour evolution by using numerical simulation and test. The main contents are as follows:(1) Numerous events of bridge damaged due to the local scour were reviewed. this paper in the background of real engineering shows that change of flow field distribution around piers is important to study the mechanism of local scour.(2) Based on principle of computational fluid dynamics, the commercial software, Fluent, was utilized to simulate the3D flow field around the pier during the local scour evolution. In order to close the RANS equations, the RNG κ-ε turbulent model combing appropriate wall treatment method were used.(3) The numerical model was validated by measured data of flow velocity in plane bed conditions, and the complicated flow structure around the pier on plane bed was analyzed. The horseshoe vortex system around the pier was obtained by numerical simulation.(4) The dimensions of scour hole at different times were measured, which were used as the boundary conditions of numerical model. The calculation results reveal the variation of flow velocity, riverbed shear stress, vorticity and turbulent kinetic energy development.(5) The horseshoe vortex, the accelerate flow and wake vortex are the main dynamic factors resulting in the local scour around bridge pier. At early stage of scour, the accelerate flow contribute to local scour dominantly; while, with the development of scour hole, the action of horseshoe vortex system is relatively with accelerate flow. In the behind of pier, the velocity is small, while turbulent fluctuation is strong under the impact of wake vortex which results in the scour development there.