Leading-edge surface contamination effects on boundary-layer separation and wake dynamics of a low-Reynolds-number wind turbine blade

This study investigates the aerodynamic impact of leading-edge surface contamination on a NACA 63₍₃₎-418 horizontal-axis wind turbine blade section operating in a low-Reynolds-number regime. While conventional high-Reynolds-number aerodynamics characterises surface roughness as strictly detrimental, this research evaluates the regime-dependent potential of surface roughness to act as a beneficial flow-control mechanism. Utilising Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD), we quantified the effects of varying roughness severities (P80 and P40 grits), suction-side chordwise extents (2 %, 6 %, and 10 %), and contamination densities (3 % and 4 %). Results demonstrate an angle of attack (α) dependent dual aerodynamic response. In the pre-stall regime (α ≤ 4°), leading-edge roughness acts as a parasitic disturbance, forcing premature boundary layer transition and increasing the recirculation area by approximately 35 % compared to the clean baseline. Conversely, at the transitional angle of α = 8°, coarser P40 grit reduced the recirculation area by 94 % relative to the clean baseline recirculation area. This was achieved by inducing a micro-recirculation bubble that injected turbulent kinetic energy into the near wall region, forcing rapid flow reattachment. Under deep stall conditions (α = 12°), restricting the finer P80 grit to a 2 % suction-side extent at 3 % contamination density proved optimal. This configuration injected concentrated near-wall turbulent kinetic energy (TKE), delaying separation from x/c ≈ 0.16 to x/c > 0.9. These findings reveal that highly localised degradation functions effectively as a passive stall-delay mechanism. Critically, for condition-based maintenance of low-speed rotors, the chordwise extent of leading-edge contamination is a more aerodynamically significant parameter than its mere presence.