Effect of bio-inspired serrated flap on the aerodynamic performance and noise of wind turbine airfoils

To achieve synergistic optimization of aerodynamic performance enhancement and noise suppression for wind-turbine airfoils, this study proposes the bio-inspired serrated flap (ABSF) concept. Based on the S809 baseline airfoil, the design integrates a high-performance flap inspired by the shortfin mako caudal fin with trailing-edge serrations derived from owl wing morphology. Numerical simulations were performed across the specified independent parameter ranges, with serration height hs varied from 0.8%c to 2.0%c and flap deflection angle θ varied from 30° to 90°, to evaluate aerodynamic and acoustic performance and to elucidate the governing mechanisms. The flap alone (ABSF-0–45°) improves aerodynamic performance but markedly degrades acoustic performance. Adding serrations both enhances aerodynamic performance and offsets this acoustic penalty. Within the tested parameter range, ABSF-1.6–45° attains the best compromise between aerodynamic gain and noise reduction: at α = 6°(the maximum lift-to-drag ratio condition), the lift-to-drag ratio increases by 10.16% relative to the baseline, while the average overall sound pressure level (OASPL) of surface-radiated noise falls by 3.83 dB. At α = 14°, the OASPL remains reduced by 2.21 dB. For wake noise, ABSF-1.6–45° yields notable suppression at α = 6° and α = 10° but its effectiveness diminishes at α = 14°. Mechanism analysis indicates that ABSF-0–45° increases spanwise coherence of trailing-edge shedding and slows vorticity decay, thereby elevating radiated noise, whereas ABSF-1.6–45° reorganizes large trailing-edge vortices into smaller, less spanwise-coherent structures with faster vorticity decay and a more orderly spatial distribution, thus substantially reducing source strength while preserving aerodynamic gains.