Measurements of flow-induced vibration of C- and D-section prisms in a free stream flow

The cross section of a bluff body free to undergo flow-induced vibration plays a critical role in its vibration characteristics. The physics behind the driving force changes altogether, depending on the cross-sectional geometry. While the curved surface allows flexible separation points, the sharp-edged geometry has fixed locations of flow separation. The D- and C-section prisms that fall into both categories offer hybrid dynamics depending on their orientations and flow conditions. This motivated us to examine the above-mentioned test specimens, especially the role of the cavity of the C-section prism. We experimentally investigate the flow-induced vibrations and the energy harvesting performance of circular, C-, and D-section prisms (closed and open semi-circular cylinders) in a reduced velocity range of 2–16 and a Reynolds number range of 1500–10 500. We discuss the response of the test specimen using displacement amplitude, fluid forces, and power spectral density of the two. The response of the D- and inverted C-section prism is indistinguishable, suggesting no active role of the cavity when placed as the front body. These configurations show a combined vortex-induced vibration (VIV)—galloping response. However, the inverted D-section prism shows a pure VIV response with no lower branch. A notable finding of this study is that the C-section prism, with the cavity as the afterbody, produces negligible vibration amplitude, thereby mitigating VIV. In addition, the energy harvesting efficiency of all test sections is compared, and the D-section prism is found to be most efficient.