Aerodynamic Performance and Mechanistic Analysis of a Maple-Samara-Inspired Small Wind Turbine Rotor.

Abstract

Spinning samaras provide a promising biological basis for small wind turbine rotors, but the engineering translation of their three-dimensional morphology and the mechanisms governing performance losses below and above the low-tip-speed-ratio optimum remain insufficiently understood. In this study, a small horizontal-axis wind turbine rotor was developed from a µCT-informed engineering reconstruction of an Acer buergerianum samara. Its aerodynamic performance was evaluated using transient URANS simulations with the SST k-ω model and a sliding mesh, supported by grid and time-step sensitivity studies and validation against NREL Phase VI torque measurements. At U = 5 m/s and λ = 3, increasing the blade number from two to five raised C_p from 0.2445 to 0.3767, whereas a sixth blade provided only a further 1.01% increase. Among the sampled pitch angles, β = 20° produced the highest C_p of approximately 0.388. For N_b = 5 and β = 20°, a refined sweep identified a near-flat peak over λ ≈ 3.0-3.25 and a high-efficiency interval defined by C_p/C_p,max ≥ 0.90 of λ ≈ 2.28-3.70. For the same configuration, C_p at λ = 3 increased from 0.3698 to 0.4021 as Re_0.75R increased from 1.23 × 10^5 to 3.69 × 10^5. Mechanistic analysis showed that the peak is sustained by a continuous positive power-contribution band over the mid-to-outer span. At low TSR, suction-side separation, near-wake recirculation, and axial-velocity deficit restrict the effective work-producing region; at high TSR, viscous resisting torque largely cancels the pressure-driven torque. Together, these findings explain the low-TSR peak and provide mechanism-based guidance for blade-number selection and TSR control of the present samara-derived rotor.