Free-stream Turbulence Effects on Long-span Bridge Aerodynamics

Abstract

The importance of vortex induced vibrations (VIV) in the design of bridge decks is becoming more apparent (Wu and Kareem, 2012). Generally, experimental literature presents a bridge deck situated in a smooth flow, though bridges are usually subjected to the inherent turbulence of atmospheric wind. According to the results of Matsumoto et al. (1993), the effects of turbulence on VIV are rather complicated, this is mainly due to an interaction between the vortices in the wake, and vortices induced by the structure motion. The impacts of turbulence on the motion-induced forces are uncertain due to a limited understanding of this issue. Wu and Kareem (2012) also present a conjecture, suggesting that turbulence can enhance or diminish the structural response, depending on whether the dominant vortices are generated from the motion of the structure, or vortex shedding in the wake. This numerical investigation aims to verify this hypothesis, while studying the effects of turbulence on the structural response, aerodynamic forces, correlations, and wake characteristics for a dynamic bridge deck. Some effects of freestream turbulence on a rectangular bridge deck undergoing VIV are presented. Heaving motion of the model under a smooth flow is presenting with a peak r.m.s. response y/D∼3% in a close agreement with the equivalent wind tunnel experiment. Introducing turbulence into the flow reduces the peak rms response by 50%, which is in accordance with observations in the literature. This abstract also reports the effects of turbulence on the spanwise correlation of pressure on the bridge deck surfaces. Due to the dominance of the structural motion, the correlations for the dynamic cases at lock-in were markedly increased in comparison to the equivalent static case. The presence of turbulence has also shown to reduce the correlation across the span for both static and dynamic cases. It can therefore be deduced that turbulence reduces the strength of the leading edge (motion-induced) vortices of the structure, and accordingly its VIV response. Sensitivity studies of the effects of turbulence intensity and integral length scales were conducted. Effects of turbulence on the pitching motion were studied as well. Detailed results will be reported in the conference.