Experimental investigation of partial-span slot effects on small-scale horizontal-axis wind turbines

This study experimentally investigates the influence of slot mechanisms on the power performance of a small-scale horizontal-axis wind turbine (ss-HAWT). A total of five rotor blade configurations were evaluated, including a baseline model (B1) and four slot-modified variants (M1–M4), each incorporating full- or partial-span (based on root-based, tip-based) slot geometries at distinct spanwise locations. The implemented slot mechanism was defined by three novel slot radii, the slot inlet pressure side radius (r p ), the slot outlet suction side radius (r t ), and the Coanda radius (r c ), which were designed. Experiments were conducted in an open-test-section, blowing-type wind tunnel under two rotational speeds (300 and 400 rpm). Surface oil flow visualization (SOFV) was employed to analyze the blade surface flow topologies and identify regions of attached flow on both suction and pressure sides. The M1 configuration, featuring a full-span slot configuration, consistently demonstrated superior power coefficient (C P ) values across all tip speed ratio (λ or TSR) values at 300 rpm. The full-span slot design (M1) yielded a maximum C P of 0.46 at λ = 3.9, corresponding to a 9.5 % improvement over B1 at 400 rpm. The results revealed that slot integration notably delayed flow separation and promoted surface attachment, particularly in the tip region, thereby extending high-efficiency operation to higher TSR regimes. The findings confirm that strategically slot mechanisms offer a robust aerodynamic improvement for ss-HAWT.