Overall design optimization of dedicated outboard airfoils for horizontal axis wind turbine blades

Abstract

Designing the primary airfoils for the outboard part of wind turbine blades is a complicated problem of balancing structural, aerodynamic, and acoustic requirements. This paper presents an optimization method for the overall performance of outboard wind turbine airfoils. Based on the complex flow characteristics of the rotor blades and the varying requirements along the span of a blade, the design principles of outboard airfoils were investigated. The requirements for improving the structural performance and reducing the aerodynamic noise were combined with the following aerodynamic design considerations: high efficiency, low extreme loads, stability, and a wide operating region. Thus, this paper proposes a new mathematical model for overall airfoil optimization using the airfoil performance evaluation indicators. Then, an integrated optimization design platform is established for outboard airfoils. Through 2 design cases, new airfoils with desirable aerodynamic characteristics and improved overall performance were obtained.Comparisons between the new airfoils and reference airfoils based on numerical predictions indicate that the proposed method with the newly established mathematical model can effectively balance the complex requirements of the airfoil and improve its overall performance. More notably, the design cases also indicate that the established optimization design method can be used to address special designs of outboard airfoils for different blade requirements. KEYWORDS evaluation parameters, horizontal axis wind turbine, integrated design platform, numerical optimization method, outboard airfoils, overall performance 1 | INTRODUCTION Dedicated airfoils for horizontal axis wind turbines (HAWTs) have evolved over the past several decades and have received increasing attention in recent years because of the increasingly complex aerodynamic and structural requirements of the rotor blades. The airfoil is the profile of the blade cross section, and its performance determines the energy capture performance of the blade. Special airfoils for wind turbines were initially designed in the 1980s. 1 Later, they were intensively developed by the National Renewable Energy Laboratory (NREL), 2 TU Delft, 3 and RISØ, 4 and they have recently nearly replaced traditional aviation airfoils in blade designs. However, with the development of upscaling rotor blades and regional wind farms, the efficient design of special blades operating in different conditions requires advanced airfoils with improved overall performance.Specifically, design methods for improving the overall airfoil performance need to be developed.The early airfoils specially created for wind turbines were designed using the inverse method. 5,6 With the help of subsonic, low Re flow solvers, 7-9 researchers developed some commonly used wind turbine airfoils. However, the inverse design method cannot effectively address the multiobjective design problem. The objectives mainly focused on several aerodynamic force coefficients, such as c l,design or l/d max ...

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“…The introduction of this parametric method has been detailed in literature. 27 The input variables were listed in Table 1. Figure 1 shows all the input factors of the airfoil geometric parameterization.…”

“…An airfoil optimization framework was previously presented by the authors 27,43 This paper in further integrated the DOE method, airfoil geometry design method, aerodynamic-structural-acoustic analysis method, performance evaluation method, and post-processing method and finally established a new airfoil DOE platform. The framework of this platform is shown in Figure 3.…”

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