Effect of span wise airfoil profile variation combination and tip modification with winglet on wind turbine blade performance under site specific wind condition

The aerodynamic performance of wind turbine blades depends on airfoil choice, span-wise distribution, and tip design. While low-Re airfoils have been studied extensively for small HAWTs, the combined effects of mixed-airfoil configurations and tip modifications remain less explored. This study compares baseline, mixed-airfoil and tip-modified blades, linearized and winglets, to optimize efficiency and AEP. Analysis employed BEM, QBlade, and CFD (k–ω SST), supported by wind tunnel validation using scaled blades tested over 0–90° AoA and 2.8–25.2 m/s inflow velocities. Results demonstrated good agreement between CFD and experimental data, particularly below stall, though CFD slightly under-predicted lift at low Reynolds numbers. Mixed-airfoil configurations yielded notable performance improvements: mean lift-to-drag ratios reached 93.45 with the EYO9–8 tip, surpassing the baseline (74.02) by 26.25 % while with tip modification reaches 32.70 %. Winglets further enhanced aerodynamic efficiency, providing torque gains of 1.7 % and thrust increases of 1.3% compared to unmodified tips. The power coefficient (Cp) improved to 0.50 for SG6043 and EYO9–8 tips, relative to 0.49 for the baseline design. AEP analysis shows site-specific advantages: Adama (moderate k) achieves higher absolute AEP but smaller relative gains (4.30–5.68%), while Itaya (high k) yields lower absolute AEP but stronger tip-modification benefits (6.96–8.53%). The integrated use of BEM, QBlade, CFD, and experiments confirms that mixed-airfoil distributions with tip modifications reduce vortex drag, improve performance, and enhance AEP, offering a scalable design framework for next-generation wind turbines.