###### Abstract  
Sustainability has become one of the most significant considerations in everyday work, including energy production. The fast-growing trend of wind energy around the world has increased the demand for efficient and optimized airfoils, which has paved the way for energy harvesting systems. The present manuscript proposes an aerodynamically optimized design of the well-known existing NREL S809 airfoil for performance enhancement of the blade design for wind turbines. An integrated code, based on a genetic algorithm, is developed to optimize the asymmetric NREL S809 airfoil by class shape transformation (CST) and the parametric section (PARSEC) parameterization method, analyzing its aerodynamic properties and maximizing the lift of the airfoil. The in-house MATLAB code is further incorporated with XFOIL to calculate the coefficient of lift, coefficient of drag and lift-to-drag ratio at angles of attack of 0\({}^{\circ}\) and 6.2\({}^{\circ}\) by the panel technique and validated with National Renewable Energy Laboratory (NREL) experimental results provided by The Ohio State University (OSU). On the other hand, steady-state CFD analysis is performed on an optimized S809 airfoil using the Reynolds-averaged Navier-Stokes (RANS) equation with the K-\(\omega\) shear stress transport (SST) turbulent model and compared with the experimental data. The present method shows that the optimized airfoil by CST is predicted, with an increment of 11.8% and 9.6% for the lift coefficient and lift-to-drag ratio, respectively, and desirable stability parameters obtained for the design of the wind turbine blades. These characteristics significantly improve the overall aerodynamic performance of new optimized airfoils. Finally, the aerodynamically improved results are reported for the design of the NREL Phase II, Phase III and Phase VI HAWT blades. wind turbine airfoil; aerodynamic shape optimization; airfoil; class shape transformation (CST); PARSEC; optimization; genetic algorithm; CFD simulation +
Footnote †: journal: Applied Sciences  
2030 [8]. However, harnessing wind energy to its fullest is limited by several constraints: large land occupancy, high installation costs, land requirements, noise pollution and the structural limitations of the wind turbines. Therefore, to optimize the efficiency of the wind energy systems, different design concepts or optimized airfoils are needed for the blades to maximize their lift and lift-to-drag ratios. In recent years, several design concepts for wind energy systems have included high-altitude wind energy converters (HAWECs) and airborne wind energy (AWE). Aerodynamic shape optimization (ASO) has become important for development in the aerospace and mechanical engineering fields. The aerodynamic shape parametric method, by obtaining an optimized result, plays an important role in ASO [9]. The parametric method with fewer design parameters is efficient, less time-consuming during optimization and has the capability to handle a large, aerodynamic shape in the design space. Earlier, different types of aerodynamic shapes were designed with different aims and objectives. As we are moving toward the industrial revolution and transformation of new CFD techniques, different numerical tools are developed for the optimization of airfoils, instead of using the old flat plate theory for the design of airfoils [10]. For the design of airfoil aerodynamics, the two main approaches are (1) inverse design (ID) and (2) direct numerical optimization (DNO) [11; 12]. The ID method is used to solve the geometry and search different airfoil designs, which can satisfy the fluid dynamic structure and generate pressure distribution. DNO acts as a coupled geometry and performs aerodynamic analysis to generate an optimum design in an iterating process related to different objectives and constraints.