Numerical investigation on vortex-induced vibration response of the bionic cylinder inspired by Euphorbia trigona

Inspired by the morphological characteristics of Euphorbia trigona , the vortex-induced vibration (VIV) responses of the bio-inspired cylinders at different angles of attack are systematically investigated through numerical methods. A standard smooth circular cylinder is adopted as the reference configuration (T 0 ), and the bio-inspired configurations are examined at angles of attack of 0° (T 1 ), 30° (T 2 ), and 60° (T 3 ). The VIV response of T 1 is significantly suppressed compared with that of T 0 , and the maximum normalized transverse and in-line displacements are reduced by 92.8% and 90.9%, respectively. In contrast, the large-amplitude motions are observed within the high reduced-velocity range for T 2 and T 3 , with T 2 exhibiting enhanced in-line vibration and T 3 showing substantially enhanced transverse vibration. However, the vortex-shedding frequency is effectively regulated for T 2 and T 3 . The maximum normalized in-line displacement of T 2 reaches 1.70, while the maximum normalized transverse displacement of T 3 reaches 6.53, corresponding to increases of 415% and 327%, respectively, compared with that of T 0 . Further analysis of the attack angle dependence identifies 30° as a critical angle for the onset of large-amplitude galloping-type response. The distinct vibration characteristics are attributed to the angle-dependent asymmetric interaction among the three ribs, which modifies the flow separation, secondary vortex separation, wake structure, and pressure distribution around the cylinder. In particular, the rear ribs of T 1 generate a relatively uniform low-pressure region that weakens transverse pressure fluctuations, whereas the asymmetric rib interactions in T 2 and T 3 promote secondary separation and pulsating low-pressure regions, thereby enhancing fluid–structure coupling. These findings demonstrate that the three-rib bio-inspired geometry can provide an angle-dependent approach for either suppressing or enhancing VIV, offering potential applications in vibration mitigation and flow-induced energy harvesting.