Publication
The present study uncovers how a Gyroid-structured extension, attached to a hydrofoil trailing edge, may prevent the formation of Karman vortices and remarkably reduce vortex-induced vibration (VIV). The case study is a blunt truncated NACA 0009 hydrofoil of 100 mm chord length and 150 mm span, placed in a water stream at high Reynolds number (Re = 0.6 × 106 to 2 × 106). In the absence of the Gyroid extension, as the flow velocity is increased from 6 to 20 m/s, the alternate Karman vortices generated in the wake are responsible for the hydrofoil vibration with a strong torsional lock-in at flow velocities ranging from 15 to 17 m/s. The Gyroid extension, however, largely reduces the flow-induced vibrations and the lock-in is completely suppressed. Specifically, the RMS value of the surface velocity signal is cut by 67% under lock-off conditions and 99.5% under lock-in conditions. Detailed velocity measurements in the wake using laser Doppler velocimeter confirm that the Gyroid insert eliminates the frequency peak associated with the Strouhal shedding frequency and reduces broadband noise excitation. These measurements uncover how the combination of porosity and tortuosity of the Gyroid insert prevents the formation of coherent and periodic Karman vortices. In particular, we found that the Gyroid extension is responsible for the generation of streamwise and transverse jets, which extend into the far wake, inhibiting the roll-up of transient vortices in a remarkable way. We believe that this is the key mechanism in suppressing vortex shedding. Interestingly, the measurement of lift and drag forces did not reveal any significant alteration of the hydrodynamic performances of the hydrofoil with the Gyroid extension. These promising results have far-reaching implications for the design of mechanical structures subjected to VIV, such as aircraft wings, marine propellers, hydraulic pumps, and turbines among others. The potential benefits include reduced noise emissions and mitigated fatigue risks.