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a b s t r a c tThis paper describes a multi-objective optimization method for the design of horizontal axis wind turbines using the lifting surface method as the performance prediction model. The aerodynamic code for the design method is based on the lifting surface method with a prescribed wake model for the description of the wake. A multi-objective optimization algorithm approach is employed for the optimization of wind turbine blades with 3D stacking line (swept leaned blades). The (NSGA II) Nondominated sorting genetic algorithm II is used to facilitate the multi-objective optimization and to find the global optima of high-dimensional problems. The scope of the optimization method is to achieve the best trade off of the following objectives: maximum of annual energy production and minimum of blade loads including thrust and blade rood flap-wise moment. To illustrate how the optimization of the blade is carried out the procedure is applied to NREL Phase VI rotor. The result shows the optimization models can provide more efficient designs.

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Unsteady aerodynamic characteristics of the National Renewable Energy Laboratory S809 airfoil, undergoing sinusoidal pitch oscillations at various reduced frequencies, mean angles of attack, and pitch oscillation amplitudes at Re = 106, are investigated through solutions of two-dimensional Navier—Stokes equations. It is found that there is an encouraging agreement between the computational fluid dynamics (CFD)-predicted aerodynamic force coefficient hysteresis loops and the Ohio State University wind tunnel experimental data, although discrepancies still exist at higher angles of attack and during downstroke pitch motion. The effects of some parameters are studied, and the flow behaviour and dynamic stall vortex development of a typical case are represented in great detail by streamline distribution and pressure coefficient plots. CFD methodology is proved to be promising in predicting airfoil dynamic stall characteristics, and the impact of dynamic stall on the practical operation of wind turbines is analysed. It is necessary to take this into consideration in the prediction of wind turbine performance.

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Small wind turbines usually operate in sub-optimal wind conditions in order to satisfy the demand where it is needed. The aerodynamic performance of small horizontal axis wind turbines highly depends on the geometry. In the present study, the geometry of wind turbine blades are optimized not only in terms of the distribution of the chord and twist angle but also with 3-dimensional stacking line. As the blade with 3-dimensional stacking line is given sweep in the plan of rotation and dihedral in the plan containing the blade and rotor axis, the common used blade element momentum method can no longer provide accurate aerodynamic performance solution. A lifting surface method with free wake model is used as the aerodynamic model in the present work. The annual energy production and the starting performance are selected as optimization objective. The starting performance is evaluated based on blade element method. The optimization of the geometry of the non-straight wind turbine blades is carried out by using a micro-genetic algorithm. Results show that the wind turbine blades with properly designed 3-dimensional stacking line can increase the annual energy production and have a better starting behavior compared with 2-dimensional-optimized blade geometries.