Studies on Unsteady Aerodynamic Forces on Vehicles under a Fluctuating Side-wind

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The response of aerodynamic forces( a side and a drag forces ) on a vehicle model passing through a wake behind a main tower of a big suspension bridge has been investigated in a wind tunnel. A new device that makes a vehicle model run with a high speed has been constructed. We successfully extract a component due to a vortex-street from the unsteady side and drag forces on a vehicle model which has been neasured at the same time with an unsteady pressure on the side surface of a tower model. As additional experiments, a splitter-plate placed behind the tower model prevents the vortex street from shedding in the wake. Which makes the effects of the surviving velocity-gradient clear and a side and a drag forces on a vehicle which suddenly immerges in a uniform flow also has been measured.Then we have prepared five vehicle models: three cylindrical (2-dimensional) models and two box (3-dimensional) models with a rectangular and a aquare sections, respectively. The results of the present … More study may be summarized as follows: (1) When a cylindrical model passes through the wake of the tower with a splitter plate, the aerodynamic forces are influenced by the effects of an apparent angle of attack, the interference between the flows around a tower and a vehicle, and the effects of transient characteristics of flow. In the case of box models, the aerodynamic forces are governed by the effects of the angle of attack. (2) The fluctuation in a side-force exerted on a cylindrical or a box models corresponds to the fluctuation in a wind velocity due to the vortex-street behind a tower, and the unsteady forces with a constant phase-angle referred to the vortex-movement remarkably increase when the cehicle gets out of the wake. (3) The unsteady forces on a box model respond more rapidly to the cahnge in wind velocity than ones on a cylindrical model. (4) The periods of the unsteady forces on the vehicles are found to get out of order influenced by its passing through the vortex-street. Less