Effects of the flexible vortex generators on vortex-induced vibration of a simplified separated-box girder

This study investigates the influence of flexible vortex generators (FVGs) on the vortex-induced vibration (VIV) of a simplified separated-box girder (SBG) comprising twin rectangular cylinders. Each cylinder has a width (D) of 70 mm, an aspect ratio (B/D) of 4, and a gap ratio (G/D) of 2. The Reynolds number ranges from 1.03 × 10⁴ to 5.96 × 10⁴ based on the oncoming flow velocity and D. Two-dimensional FVGs, measuring 35 mm in length and 0.06 mm in thickness were vertically clamped at the leading and/or trailing edges of the rectangular cylinders. Synchronized pressure–vibration measurements and flow visualization reveal the mechanisms by which the FVGs suppress VIV. The results indicate that the clamping position and flapping state of FVGs are critical factors influencing VIV. Trailing-edge FVGs, subjected to forced oscillations that synchronize with the motion of SBG during VIV, enhance local pressure fluctuations near the trailing and leading edges of the upstream and downstream cylinders, respectively. This characteristic significantly increases VIV amplitude and lock-in range. Conversely, leading-edge FVGs generate flapping-induced vortices (FIVs) through periodic flapping. This process disrupts the separation pattern of the leading-edge shear flow, thereby effectively suppressing VIV. The mechanism lies in FVGs continuously entraining high-speed fluid toward the cylinder side walls through periodic flapping, enhancing momentum exchange between the freestream and separated regions near the cylinder, thereby achieving effective VIV suppression.