水平軸式風力機葉片運轉於高轉速或承受高風速時會產生嚴重的失速現象，此時傳統型葉片元素動量理論已經無法精確的針對運轉中失速區域的葉片進行性能之預測。因此本研究先利用相關之修正因子加入傳統型葉片元素動量理論，如葉尖修正因子(tip-loss factor)、失速延遲模型(stall delay model)與VC失速模型(Viterna-Corrigan stall model)。三種不同操作型態之葉片將被驗証於改良型葉片元素動量理論。其中兩款為國家能源再生實驗室(National Renewable Energy Laboratory, NREL)所開發出之水平軸式風力機定速型操作系統，另一款為國立成功大學(National Cheng Kung University, NCKU)所開發之四百瓦水平軸式風力機變速型操作系統。其功率曲線結果與風洞實驗數據比對後，可証明改良型葉片元素動量理論可得到良好的結果。
在証明改良型葉片元素動量理論的可行性之後，持續再利用該理論設計出於額定風速(rated wind speed)為10 m/s與設計周速比(design tip speed ratio)為5時之水平軸式風力機葉片，該葉片之斷面形狀是使用NACA4418之翼型，直徑為0.72 m，每斷面於設計點之下可得到最佳之節距角(pitch angle)與弦長(chord length)之分佈。另一款葉片有最佳節距角分布但無最佳弦長分布，最後一款葉片為無節距角與弦長之分布。三款不同幾何形狀之葉片將同時進行全尺寸之風洞測試。
最後，本研究也利用數值模擬之方法進行驗證，並觀察改良型葉片元素理論與風洞測試所無法觀察之流場部份。發現數值模擬之方法可準確的計算出水平軸式風力機葉片之性能，並可有效並簡易的觀察流場現象。

Due to occurrence of blade stall at high wind speed or high rotational blade speed of a wind turbine, the blade element momentum (BEM) theory based on the given aerodynamic performance data of airfoil will become inaccurate for the performance prediction of a horizontal-axis wind turbine (HAWT) blade. Therefore, in this study the BEM theory is incorporated with the proposed tip-loss factor, Viterna-Corrigan stall model and stall delay model to improve the accuracy and applicability for wind turbine blade performance prediction. To verify the proposed method of the improved BEM theory, three different types of operation and geometry of HAWT blades are used and compared to justify the proposed method. Two wind turbines developed by National Renewable Energy Laboratory (NREL) are operated at the constant rotational speed but with different blade geometry design, while another wind turbine has been developed in National Cheng Kung University (NCKU) is operated at the variable rotational speed with the turbine blades tapered and twisted. Results clearly indicate that the prediction of the power curves from the proposed method can effectively match with the experimental data even in the blade stall region, which is commonly inaccurate and failed to predict the power curve of the wind turbine by the traditional BEM theory.
It is now believed that the improved BEM theory is available for the prediction of the performance of the HAWT blades Thus, there are three different HAWT blade geometries with the same diameter of 0.72 m and the NACA4418 airfoil profile that have been designed and the design conditions of the turbine blade in order to display the optimum distributions of pitch angle and chord length in each section including the rated wind speed, design tip speed ratio, number of blades and design angle of attack. The first one is an optimum (OPT) blade shape, which was obtained by the improved BEM theory, and a detailed description of the blade geometry is given here. The second one is an untapered and optimum twist (UOT) blade that has the same twist distributions with the OPT blade. The third blade is the untapered and untwisted (UUT). The wind tunnel experiment has been used to measure the power coefficient of these blades. Results indicate that both OPT and UOT blades have performed the same maximum power coefficient of Cp=0.428 but located at different tip speed ratio of λ=4.92 and λ=4.32, respectively, while the UUT blade has obtained the maximum power coefficient of Cp=0.210 at λ=3.86.
After the model tests had been undertaken, numerical simulation was performed by means of fully three-dimensional computational fluid dynamics (CFD) method using the k-ω SST turbulence model. It has been found that CFD calculations reproduced the model power coefficient almost closely. The good agreement of the three models between the measured and computed power coefficients tend to accurately prove the predictions of HAWT blade performance at full-scale conditions are also possible using the CFD method.

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