Investigation of the intrinsic characteristics of two lock-in regions in a 10:1 π-shaped deck

The π-shaped deck, as a typical blunt body, is prone to vortex-induced vibration due to the surrounding flow. However, the intrinsic characteristics of sectional vibration are frequently disregarded, leading to a lack of a comprehensive understanding of the lock-in region characteristics. Therefore, a deep analysis of the spectrum characteristics was carried out using a combination of simultaneous vibration–pressure testing and computational fluid dynamics (CFD) to gain a deeper understanding of this phenomenon. In this study, the differences between the two lock-in regions were analyzed, and it was observed that the predominant frequency of vibration increased with an increase in reduced wind velocity in a certain range. Furthermore, it was found that, in the lock-in region, when the maximum amplitude occurred, the vibration predominant frequency was greater than the natural frequency. The Strouhal number (St number) of each lock-in region generally exhibited a step-like downward trend as the frequency ratio increased. Moreover, the first lock-in region was associated with the Karman vortex street in the wake region, as well as with the slow-moving vortex on the upper surface and the two vortices on the lower surface. The long tail vortex shedding in the wake region and the single vortex on the lower surface were the key reasons for the larger amplitude of the second lock-in region when compared to the first lock-in region.