Research Article Shape Optimization of NREL S809 Airfoil for Wind Turbine Blades Using a Multiobjective Genetic Algorithm Yilei He and Ramesh K. Agarwal Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, St. Louis, MO 63130, USA Correspondence should be addressed to Ramesh K. Agarwal; rka@wustl.edu Received 27 February 2014; Revised 9 July 2014; Accepted 23 July 2014; Published 9 September 2014 Academic Editor: R. Ganguli Copyright © 2014 Y. He and R. K. Agarwal. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te goal of this paper is to employ a multiobjective genetic algorithm (MOGA) to optimize the shape of a well-known wind turbine airfoil S809 to improve its lif and drag characteristics, in particular to achieve two objectives, that is, to increase its lif and its lif to drag ratio. Te commercially available sofware FLUENT is employed to calculate the fow feld on an adaptive structured mesh using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a two-equation − SST turbulence model. Te results show signifcant improvement in both lif coefcient and lif to drag ratio of the optimized airfoil compared to the original S809 airfoil. In addition, MOGA results are in close agreement with those obtained by the adjoint-based optimization technique. 1. Introduction With recent emphasis on emission-free renewable energy, wind energy has taken a center stage in recent years with exponential growth in deployment of wind-turbines world- wide. Among wind-turbines, horizontal-axis-wind-turbines (HAWTs) are mostly deployed for power generation in Megawatt range. It is well established that the power gen- erated by a HAWT is a function of the number of blades, the   /  of the blade airfoil section, and the tip speed ratio  (= rotational speed of the blade at tip/wind speed in free stream). Tus, one of the goals of the design of a wind turbine blade is to maximize its   /  . As a result, there has been signifcant efort devoted in recent years to shape optimization of wind turbine blade to achieve high   /  . In last two decades, aerodynamic shape optimization has become an important tool in aircraf design [1–4]. Te focus of this paper is on the aerodynamic shape optimization of airfoil sections used in wind turbine blades since they afect their aerodynamic performance which in turn infuences the amount of power a wind turbine can generate [5]. In modern wind-turbines, thick airfoils such as NACA- 63XXX and NACA-64XXX are frequently used; however, new airfoil families are increasingly being developed because of multiple requirements of aerodynamics performance at rated power conditions and of-rated power conditions as well as strong structural properties [6]. National Renewable Energy Laboratory (NREL) has developed a family of airfoils for HAWT applications [7] since 1984. Te present paper focuses on the optimization of most well-known NREL airfoil, known as the S809 airfoil. Tis airfoil is 21% thick laminar fow airfoil whose design and experimental results are given in [8]. NREL Phase II, Phase III, and Phase VI HAWT blades are composed of S809 airfoil from root to tip [9]. Under class 3 to 4 wind conditions, S809 is subjected to low Mach number (almost incompressible) fow with Reynolds numbers in the range of one to two million. Laminar separation can occur on the suction surface for angles of attack ranging from zero to 5.13 degrees. Turbulent trailing edge separation occurs when angle of attack increases [10]. Tis paper presents shape optimization of S809 airfoil using a multiobjective genetic algorithm (MOGA). Te com- mercially available sofware FLUENT is used for calculation of the fow feld using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a two-equation − SST turbulence model. Using MOGA, globally optimal S809 airfoil shape is obtained which maximizes both   and   /  for a given wind speed, rotational speed, and pitch setting. Te results show that the aerodynamics characteristics of Hindawi Publishing Corporation International Journal of Aerospace Engineering Volume 2014, Article ID 864210, 13 pages http://dx.doi.org/10.1155/2014/864210