Computational study and field implementation of methods for the control of vortex shedding from a bridge caisson

The precise placement of bridge caissons in fast-moving currents poses particular difficulties due to the occurrence of vortex shedding from these typically bluff structures leading to significant side-to-side oscillations. In this paper, we report on computations performed in order to recommend to a structural engineering team two practical adaptations to their caisson design in order to reduce the impact of vortex shedding from it. The adaptations involve the rounding of the sharp corners of the original caisson design together with the installation of a splitter plate of a suitable length at its base. The rounding of the corners reduces the available working space inside the caisson and this imposes a constraint on the process of finding the optimal dimensions of the proposed adaptations to yield worthwhile benefits at acceptable cost. The Unsteady Reynolds-Averaged Navier-Stokes (URANS) computational approach was used. Discretization was with second-order accurate spatial and temporal schemes while the effects of turbulence were accounted for with a turbulence model that has been extensively validated in benchmark flows with vortex shedding. The recommended adaptations were integrated in the caisson's final design and were implemented in the field. In situ velocity measurements obtained using a current meter mounted on a vessel, and photographic observations obtained from a drone provided a rare opportunity to validate the computations, and a clear demonstration of the efficacy of the proposed flow-control measures.