Numerical Simulation of the Flow and Local Scour Process around Single and Complex Bridge Piers

Abstract

The present work is focused on the flow and clear-water scour process around single and complex bridge piers using the computational fluid dynamics (CFD) approaches. In CFD, the use of large time steps may accelerate the simulation process but the effects of the unsteady flow structures may not be considered in the computations. In this case, the computational method is defined as a steady-state solution. In the present study, the capability and accuracy of the steady-state solution of the flow equations are investigated by employing the SSIIM code which is numerically stable for large time steps. For this purpose, several simulations were performed for different piers and bed configurations and the corresponding numerical results were compared with experimental ones obtained from referenced bibliography. Overall, the steady-state solution of the flow equations could predict fairly well the scour geometry at the upstream side and lateral sides of the bridge pier but not downstream side of the pier. Moreover, the local scour around a single pier was also predicted by performing an unsteady-state solution (where the vortex shedding effects are taken into account) by using the Flow-3D code. The major difference between the results from the two mentioned CFD codes was observed downstream of the pier such that, compared to the physical model, the scour depth was under-predicted by the steady-state calculations while it was over-predicted by the unsteady-state calculations.