Multi-objective optimization of airfoil shape for efficiency improvement and noise reduction in small wind turbines

The power output of a wind turbine depends on the aerodynamic and geometrical characteristic of its airfoils, and therefore, the proper airfoil design for wind turbine blades is highly important. Furthermore, due to the usage of small wind turbines within city limits, the emitted noise is also a major issue. In the present work, “XFoil” and “NAFNoise” programs were used for flow analysis around blade cross sections (airfoils) and predicting the corresponding noise emission, respectively. Multi-objective optimization was carried out for maximizing the airfoil lift-to-drag ratio (CL/CD) and minimizing the sound pressure level. With two above objective functions and by defining decision variables along with introducing physical and engineering constraints, genetic algorithm method was applied for optimization process. Moreover, ‘Fuzzy Bellman-Zadeh’ decision-making method was applied for selecting final optimal point from Pareto front. The results of this new method of airfoil shape analysis at various wind velocities showed about 26% average increase in CL/CD and 1.11% average decrease in noise emission in comparison with that for typical highly used S822 airfoil in small wind turbines.