本研究針對本實驗室所設計的二、三、四葉小型水平軸式風機，擺設在開放式環境風洞中，以6 m s^(-1)作為均勻來流風速，透過熱線風速計及動態皮托管(Cobra probe)進行尾流逐點量測，分析其平均速度分布、紊流強度等氣動力特性。本實驗中，主要針對兩種情況進行討論：(1) 改變來流與風機放置的相對角度，分析在偏向角為0°與30°的情況下，風機尾流的發展情況。(2) 利用兩種測速計，探討在偏向角為0°的情況下，針對兩者量測結果作比較。
本研究亦有應用葉片元素動量(BEM)理論模擬近尾流區的流向速度，並與風洞實驗進行比較，可以得到近似的尾流速度分布。指出在下游 X/D=1處會最接近理論的結果，而葉尖部分產生了明顯的差異，並以四葉風機的差異區間為最小。而根據結果(1)指出在尾流分布上，30°風機除了有明顯的尾流轉向外，其尾流區寬度會縮小，且其氣動力特性皆0°風機來的較弱。結果(2)發現在尾流特性上，除了動態皮托管在垂直速度上表現出較高值外，兩者測速計得到相當一致的量測結果。此外，在能譜分析中除了觀察其紊流消散分布的趨勢，也使用紅外線雷射轉速計所測得的轉速來對照一倍旋轉頻率，結果說明兩種風速測量計皆可以量測出接近斜率為-5/3的慣性次段(Inertial subrange)。

In this study, the wake characteristics of two-blade, three-blade, and four-blade wind turbines were investigated experimentally. The experiments were carried out in an open-jet wind tunnel under a uniform incoming flow condition. Hot-wire and Cobra-probe anemometers were used to measure the mean and fluctuating quantities of turbulent flows at different locations with downwind distance. The blade element momentum (BEM) theory is used to model the streamwise velocity distribution in the near wake region and the results from the BEM theory were compared with the measurements by using a hot-wire anemometer. We carried out the wake measurements with turbines in two conditions: (a) in different yaw angles (0° and 30°) by using hot-wire anemometer, and (b) in non-yaw condition by different anemometers (hot-wire and Cobra probe).
The measurement results indicate that: (a) The yawed turbines wake have an obvious shifting phenomena and the ‘wake-region width‘ as well as wake characteristics are smaller than normal turbines; (b) The hot-wire and Cobra-probe anemometers are consistent with turbulent characteristics except the vertical velocity. The power spectrum analysis demonstrates that the turbulence dissipation rate from both anemometers measurements follows as the slope of -5/3 in the inertial subrange. The reliability of the data can be confirmed by the consistency with the first harmonic peak in the spectra plots and rotating speed from the laser tachometer.

中文摘要 I
ABSTRACT II
ACKNOWLEDGMENTS IV
CONTENTS VI
LIST OF TABLES VIII
LIST OF FIGURES IX
NOMENCLATURE XIII
CHAPTER I INTRODUCTION 1
1-1. General Background Information 2
1-2. Literature Review 3
1-3. Motivation and Objectives 8
1-4. Content of Research 9
CHAPTER II EXPERIMENTAL EQUIPMENT 10
2-1. Open-Jet Wind Tunnel 10
2-2. Models of Wind Turbine 14
2-3. Hot-Wire Anemometer 17
2-4. Cobra Probe 21
2-5. Laser Tachometer 23
2-6. Experimental Set-Up 24
CHAPTER III THEORY AND ANALYSIS METHOD 30
3-1. Blade Element Momentum Theory (BEM) 30
3-2. Sensitivity Analysis on Sampling Periods35
3-3. Analysis of Turbine Wake Characteristics37
CHAPTER IV RESULTS AND DISCUSSIONS 42
4-1. Simulation of the Wake Velocity from BEM Theory42
4-2. Experimental Results in Each Cases 45
4-2-1. Case 1: Comparison of Turbine Wakes at Yaw Conditions of 0° and 30° 45
4-2-2. Case 2: Comparison of Turbine Wakes Measured with Different Anemometers 56
CHAPTER V CONCLUSIONS 67
FUTURE PERSPECTIVE 69
REFERENCES 70
APPENDIX A 74
APPENDIX B 76

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