Experimental study on flow-induced vibration of a flexible triangular cylinder

Fluid-structure interactions response of a flexible cylinder with a triangular cross-section, fixed at both ends, placed in the test section of a re-circulating water tunnel, was studied experimentally. Flow-induced vibration (FIV) response was studied in terms of spanwise amplitudes and frequencies of oscillation in both the crossflow and inline directions for angles of attack of 0°, 30°, and 60°. The cylinder had an aspect ratio of 30 and a mass ratio of 0.8. High-speed imaging technique was employed to capture the spanwise oscillations at a reduced velocity range of U* = 0.9-21.7, corresponding to a Reynolds number range of Re= 364-6,500.  At low reduced velocities, mono-frequency excitation at the first bending mode of the cylinder was observed, and as the flow velocity was increased, the oscillations transitioned to higher modes with regions of multi-frequency excitation with contributions from both bending and torsional modes. At the angle of attack of 0°, while the onset of oscillation was delayed compared to other angles, as the flow velocity was increased, large-amplitude oscillations were observed. Flow evolution around the cylinder and in its wake was tracked and the three-dimensional vortex wake was studied in correlation with the dynamic oscillations of the cylinder.