Investigating the Impact of Geometric Variations on Vortex-Induced Performance of Bladeless Wind Turbines: A CFD Study

Bladeless wind turbines (BWTs) have gained attention for their low-cost, low-maintenance, and noise-free operation compared to conventional designs, yet their aerodynamic performance, particularly the influence of mast geometry on vortex- induced vibrations (VIV) and energy harvesting efficiency, remains insufficiently explored. While most studies focus on cylindrical masts, the role of non-circular cross- sections in urban low-speed flows is largely unaddressed. This study performs a comparative Computational Fluid Dynamics (CFD) analysis of four BWT mast geometries - two cylindrical (diameters 20 cm and 22.5 cm) and two elliptical (major/minor axes 22.5 × 11.25 cm and 25 × 12.5 cm) at wind speeds of 1, 3, and 5 m/s. Lift coefficient time histories and velocity curl contours reveal that cylindrical models produce strong, sustained periodic vortex shedding with high-amplitude oscillations, with the 22.5 cm cylinder (Model 2) exhibiting the most coherent and energetic response across all speeds, making it the most effective for VIV-based energy extraction. Elliptical models demonstrate superior aerodynamic damping; the smaller elliptical section (Model 3) achieves the strongest suppression of VIV, characterized by rapid transient decay, minimal wake vorticity, and low-amplitude oscillations, particularly at higher velocities. The larger elliptical model (Model 4) provides intermediate performance with more persistent but less intense shedding. These results highlight the critical impact of cross-sectional geometry on VIV characteristics and suggest that elliptical profiles, especially lower aspect ratios offer significant potential for vibration control, while larger cylindrical designs remain optimal for maximizing energy harvesting in small-scale urban BWT systems.