Study on vortex-induced vibration characteristics of side box <b> <i>π</i> </b>-shaped cross sections with different aspect ratios

The π-shaped cross sections with aspect ratios of 6, 8, and 10 were selected as research objects to investigate the influence of aspect ratio on vortex-induced vibration (VIV) characteristics. Wind tunnel vibration tests were conducted at angles of attack (AOA) of 0° and ±3°. In addition, for the cross section with a 10:1 aspect ratio, concurrent vibration and surface pressure measurements, as well as numerical simulations, were performed to provide detailed insight into the flow–structure interactions. Surface pressure characteristics under different AOAs are systematically analyzed using the partition method, energy method, and correlation coefficient method. Based on the correlation coefficient method, the concept of wave crest distance was proposed. The results demonstrate that an increasing trend in maximum vibration amplitude was observed with increasing aspect ratio. A delay of VIV response was observed in the lock-in region as the AOA shifted from negative to positive. From the perspective of correlation coefficients, as the AOA transitions from negative to positive values, the wave crest distance between the correlation coefficients of upper and lower surfaces gradually decreases. Correspondingly, the maximum VIV amplitude in the second lock-in region of vertical bending increases with the reduction of wave crest distance. The second lock-in region at 0° AOA is associated with the “long-tail” vortex shedding; however, when the AOA is not at 0°, the long-tail vortex shedding pattern transitions to a “thick-tail” pattern.