角柱のクロスフロー振動に対する後流平板の干渉効果

概要

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Wind tunnel experiments are carried out to investigate interference effect of downstream strip plate of width w=d on the crossflow vibration of a square cylinder with a side length d=26mm. While sufficient suppression of Karman vortex induced vibration is not attained by plates with crossflow height less than ld=4d, the galloping is suppressed even by a square plate, i.e. ld=d, when the gap ratio 1<s/d<2.0. When a plate of ld≤2d is set with a gap ratio s/d<1-1.4, a large vibration occurs at U>5m/s with the maximum amplitude at around s/d=0.3. The amplitude at s/d=0.3 increases divergently with flow velocity. Measurement of the lift force on the square cylinder and the velocity in the near wake for the corresponding fixed system shows no evidence for periodic change of flow responsible for the vibration. A prediction of this vibration based on the quasi-static hypothesis suggests that the vibration is caused by the 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.