Tip shape effects on the axial-flow-induced vibration of a cantilever rod

The influence of tip shape on flow-induced vibration of a cantilever rod subjected to axial water flow is experimentally investigated, through optical tracking of the rod movement and mapping of the instantaneous flow field around the rod tip. The experimental setup consists of a vertical cantilever rod housed within a tube. The rod tip shapes considered in this study include a blunt tip and cones with height-to-diameter ratios of 0.5, 1, and 2. The experiments were conducted across a Reynolds number range between 20k to 100k in both clamped-free and free-clamped configurations,representing opposite flow directions. The rod tip motion was captured using fast video
image tracking, whereas the flow field near the rod tip was obtained using particle image
velocimetry (PIV). The rod vibration dynamics exhibited a primarily fuzzy period-1 behavior,
characterized by a periodic motion with a chaotic component. Flutter-like oscillation and buckling
were also observed at higher Reynolds numbers, depending on the flow direction. The
mechanisms of fluid-structure interaction involved turbulent buffeting and movement-induced
excitations. Unsteady flow separation around the rod tip was identified as a further contributing
mechanism to flow excitation. In the clamped-free configuration, unsteady flow separation
was more pronounced for the cone tips due to the increased rod surface area in the wake region,
leading to larger vibration amplitude. In the free-clamped configuration, flow separation effects
were more prominent for the blunt tip, as the streamlined cone shapes were less prone to flow
separations. Overall, the rod with a blunt tip resulted in smaller displacement in the clamped-free configuration, while the rods with cone tips led to smaller displacement in the free-clamped configuration