Investigation of vortex response of a twin box bridge section at high and low Reynolds numbers

Abstract

The vortex shedding response of a twin box bridge girder deck with and without guide vanes has been investigated at three different Reynolds numbers with the objective of identifying the mode of vortex excitation and suitable conditions for testing that will allow faithful evaluation of guide vane mitigation efficiency. It has been established that the displacement thickness must be at the order of 10% of the guide vane offset in order to allow sufficient flow rate to render the guide vane efficient. Conventional section model scales ranging from 1:50 to 1:100 are not likely to be capable of fulfilling such conditions. Measurement of the fluctuating pressure field around the twin girder deck indicates that vortices shed from the upwind box will impinge on the downwind box resulting in higher fluctuating pressures here than on the upwind box from where the vortices are shed. This process is likely to render the twin deck more susceptible to vortex shedding excitation than the mono box deck.