Interference Effect of Downstream Strip-Plate on the Crossflow Vibration of a Square Cylinder

Wind tunnel experiments are carried out to investigate the interference effect of a downstream strip-plate of width w = d on the crossflow vibration of a square cylinder of side length d = 26 mm. While the vibration induced by the Karman vortex is insufficiently suppressed by plates with crossflow height less than ld = 4d, the galloping is suppressed even by a square plate, i.e. ld = d, at gap ratios 1 < s/d < 2.0. When a plate of ld ≤ 2d is located at a gap ratio s/d < 1-1.4, a large vibration occurs at U > 5 m/s with maximum amplitude around s/d = 0.3. This amplitude increases divergently with increasing flow velocity. Measurement of the lift force on the square cylinder and the velocity in the near wake for the corresponding fixed system indicates that the vibration is not caused by periodic flow changes. The quasi-static hypothesis predicts that the vibration is caused by fluid-elastic instability but not by a periodic vortex shedding. Hence, the name ‘Wake Body Interference Fluid Elastic Vibration (WBIFEV)’ is proposed for this vibration.

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