Aerodynamic Performance of an H-Darrieus Vertical-Axis Wind Turbine with a Curved Gurney Flap Under Low-Wind Conditions

This study experimentally evaluates a curved Gurney flap (GF) as a passive trailing-edge modification to improve the low-wind aerodynamic performance of an H-Darrieus vertical-axis wind turbine (VAWT). A small-scale three-bladed rotor based on a NACA 0018 profile (chord = 100 mm, diameter = 320 mm, height = 300 mm) was fabricated via fused-deposition modeling (PLA) in two configurations: a clean baseline and a curved-GF design with flap height ℎGF = 0.05с. Wind-tunnel tests were attempted at V = 3–8 m/s; however, steady-state rotation was achieved only at V = 5–8 m/s and performance metrics are reported for this range. Rotational speed was measured using a tachometer, and shaft torque was obtained using a rope brake dynamometer to compute tip-speed ratio (TSR), mechanical power, and power coefficient (Cp). Compared with the clean baseline, the curved-GF configuration increased peak efficiency, achieving Cpmax = 0.2276 at TSR = 1.10, representing a 23.43% improvement over the baseline (Cpmax = 0.1845 at TSR = 0.92). Across the steady-state test conditions, the curved-GF rotor maintained higher Cp values than the clean configuration, indicating that a curved GF can serve as a practical, low-cost passive enhancement for small VAWTs operating in low-wind regimes.