Experimental study on the vortex-induced vibration of a stepped cylinder in uniform flow

An experimental study on the vortex-induced vibration (VIV) of a stepped cylinder in uniform flow was performed, with the Reynolds number Re =450 〜6 000. The effects of the coverage ratio R and diameter ratio D/d on the vibration responses were investigated. The results show that a "transition branch，，appears in the vibration responses of the stepped cylinder when r= 25% 〜75% • On the transition branch，the amplitude increases gradually, and the lift force first increases and then decreases. With the increase of R and D/d，the reduced velocity range for the transition branch extends, while that for the initial branch shrinks. In the lock-in region, the oscillation frequency of the cylinder sequentially locks onto two frequencies with the increase of the reduced velocity, which is termed as the "dual lock-in" . There is an obvious correspondence between the lock-in regions and the response branches. © 2022 Chinese Vibration Engineering Society. All rights reserved.