Flow Characteristics of Steel Box Girder Cross-section with Non-uniformly Closed Railing
From the velocity distribution around flow field,the development and evolution of 3D vortex structures,and the pressure distribution on main girder surface,etc.,the large eddy simulation was used to investigate the influence of non-uniformly closed railings along bridge span on the flow characteristics of steel box girder cross-section,and to investigate the intrinsic mechanisms of suppressing vortex-induced vibration.The numerical simulation result shows that the aerodynamic shape of original cross-section of inclined web steel box girder has little difference in span-wise direction.When the flow field passes through the upstream railing,the vortex structure at each railing position is relatively similar.In the main flow field of vortex,the vortex structure rotates along the bridge and has obvious downwind characteristics.Under the condition of 5° wind attack angle,the influence of central railing on the vortex generated at the upstream bridge deck is very little,while the vortex size and energy detached downstream of model are larger,causing the vibration amplitude of model to be greater than that of 3° wind attack angle.The large negative pressure appears on the leeward side of upstream bridge deck if the outer railings are closed.That would induce larger downstream airflow in the span-wise direction,and decrease vortex energy in the downstream.Due to the negative pressure of bridge deck,the vortex induced from the downstream is dissipated significantly,leading to the reduced vortex-induced vibration amplitude.The result indicates that the vibration suppression mechanism of the two measures are different.Under the measure of opening-two-space and closing-one-space among the railings,the vortex has a larger component in the span direction,and the main stream down-dip consumes the surface vortex,resulting in the downwind size and energy decrease of wake first vortex.Under the measure of opening-three-space and closing-one-space among the railings,the negative pressure area of upstream bridge panel is weak and backward.The wake vortex energy is low,and the strong vortex range is minimal.The pressure difference between the upper and lower surfaces is reduced.
bridge engineeringflow characteristicslarge eddy simulationflow field analysissteel box girdervortex-induced vibration
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