Investigation of vortex-induced vibration response of rectangular prisms with various aspect ratios

Rectangular prisms are typical bluff bodies that exhibit highly unstable flow fields and have long been a focal point in vortex-induced vibration (VIV) research. By governing key behaviors such as shear layer separation, reattachment, and vortex shedding, the variation in aspect ratio alters the flow topology around rectangular prisms, thereby leading to distinct flow field characteristics and ultimately dictating the VIV responses of rectangular prisms with different aspect ratios. However, systematic investigations into VIV across a broad range of aspect ratios are limited, particularly regarding how aerodynamic geometry influences the underlying vortex dynamics. Consequently, this study presents a series of wind tunnel experiments conducted on ten rectangular models with aspect ratios ranging from 1 to 10. The experiments focused on vertical VIV, encompassing VIV response tests under multiple mass-damping ratio conditions and smoke-wire flow visualizations at wind speeds corresponding to the maximum VIV response. The results demonstrate that both the VIV response and its sensitivity to damping vary significantly with the aspect ratio. Based on these observations, the rectangular prisms are classified into two distinct aerodynamic shapes: “mass-damping sensitive” and “mass-damping insensitive” aerodynamic shapes. Flow visualization further indicates that the aspect ratio governs the evolution of the flow structure to a large extent. The shear layers formed by flow separation exhibit distinct flow characteristics on the surfaces of models with different aspect ratios, and these discrepancies provide the physical basis for the divergence in VIV responses. Based on these experimental findings, the VIV mechanisms for rectangular prisms with various aspect ratios are systematically classified.