本研究致力於水平軸風力發電機的最佳化設計流程，並將此流程應用於美國再生能源實驗室所開發的五兆瓦葉片上。在此流程中，Bézier Curves完成了翼型、弦長分布與扭曲角分布的參數化，二維翼型的氣動力計算採用XFOIL，並使用Tanger 和Kocurek的方法將局部攻角的氣動力係數外插至±180°，接著採用旋轉失速修正法去校正二維翼型氣動力計算的結果，最後根據不同的運作條件下的雷諾數，對阻力係數做修正。風力機的氣動力是採用FAST進行模擬，在本研究中以葉片上的翼型、扭曲角分布和弦長分布做交叉配對成為五種不同的參數組合，限制條件包含了翼型與葉形的幾何和葉片上的結構應力。結果顯示五種不同的參數組合在最佳化後都能夠得到年發電量的提升，其中全幾何為參數的問題在最佳化後得到最好的性能，其與原始葉片相比得到了2.491%的性能提升。

This study focuses on the process of wind turbine optimization and applies this process on the NREL 5MW. In the process, all of the parameterizations are done by the Bézier Curves and the 2D aerodynamic coefficients of airfoils are estimated by the XFOIL. The Tanger and Kocurek’s method is utilized to extrapolate the 2D aerodynamic coefficients. Moreover, this study also adopts the rotational stall delay correction and the drag correction to revise the 2D aerodynamic coefficients. The aerodynamics of wind turbine is simulated by FAST. This study discusses five cases. The annual energy production is served as the objective function in the process, while the control points of the twist angle distribution, the control points of chord length distribution, the control points of twist angle and chord length distribution, the control points of airfoils and control points of full geometry are served as variables separately in each case. Constraints are adopted to limit the geometry of airfoils, the shape of the blade and the structural strength of the blade. The result shows that all cases successfully increase their AEP. after the process executes. The greatest enhancement is 2.49% in the case which uses control points of full geometry as variables.

List of Figures v
List of Tables vii
Introduction 1
1.1 Introduction 1
1.2 Literature review 2
1.3 Motivation and Objective 3
Methodology 5
2.1 Optimization algorithm 5
2.1.1 Genetic Algorithm 5
2.1.2 SmartDO® and Robust Genetic Algorithm 7
2.2 Parameterization 8
2.2.1 Bézier Curve 9
2.2.2 Third order Bézier curve and parameterization of sectional airfoil 9
2.2.3 Approximation-Least square method 11
2.2.4 Constraints on airfoil geometry and chord length distribution 12
2.3 Two dimensional aerodynamic calculation 14
2.3.1 XFOIL 14
2.3.2 Extrapolation aerodynamic coefficient from -180° to 180° 14
2.3.3 Rotational stall-delay correction 17
2.3.4 Drag correction 18
2.4 Aerodynamics of wind turbine 18
2.4.1 Blade element momentum theory 18
2.4.1.1 One dimensional momentum theory 19
2.4.1.2 One dimensional momentum theory with rotational wake 21
2.4.1.3 Blade Element Theory 23
2.4.1.4 Blade Element Momentum Theory- combine with One Dimensional Momentum and Blade Element Theory 26
2.4.2 Fast and AeroDyn 28
2.4.3 Annual energy production 28
2.5 Bending stress calculation in extreme condition 30
2.5.1 Moment of inertia 30
2.5.2 Calculation of bending stress 31
Optimization process 32
3.1 Pre-optimization 32
3.2 Process for twist angel, chord length and airfoil optimization 33
Result and discussion 36
4.1 Baseline geometry 36
4.2 CASE A: Twist angle distribution only 40
4.3 CASE B: Chord length distribution only 45
4.4 CASE C: Twist angle and Chord length distribution 51
4.5 CASE D: Airfoil shape only 56
4.6 CASE E: Airfoil shape, twist angle and chord length distribution 68
Conclusion 81
Reference 83

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