- 學位論文
U形掠角葉片幾何外形對H-Darrieus型垂直軸風力機性能之影響
Influence of U-shaped swept blade geometry on the performance of H-Darrieus vertical axis wind turbines
摘要
風力機是邁向淨零碳排未來的重要基礎設施，其中垂直軸風力機的應用場合是最有彈性的，但垂直軸風力機相對水平軸式能產生之扭矩較低，因此仍有繼續探索性能提升方法的必要性。本研究將葉片掠角起始位置比(α)及掠角偏移量(ΔV)兩參數納入考慮，目的是尋找兩參數對氣動性能之影響及其背後原理。選用之垂直軸風力機為3葉片式H-Darrieus型風力機，翼型為NACA 0021對稱型，轉子直徑為1.03 m，翼展長度為1.456 m，並透過計算流體力學求得風力機氣動性能。本研究使用k−ω SST紊流模型，採用ANSYS Fluent執行數值模擬，首先執行模擬合理性驗證，與前人數據比對確認模擬設定正確後，進行網格獨立測試，選用取足夠精準又不花費太多計算時間的網格設定。 結果發現，後掠葉片在所有情況皆可產生較大的扭矩，其中ΔV=+0.2c於α=0.25~0.75時有最佳的氣動性能；而在α=1.00時，ΔV=+0.2c和ΔV=+0.6c之功率輸出相似。前掠葉片則有較差的氣動性能表現，藉由色階圖及流線圖可觀察到前掠葉片在上風區容易出現動態失速，此現象隨掠角偏移量增加而加劇。因此整體而言，掠角偏移量較小之後掠葉片較適合作H-Darrieus型垂直軸風力機提升氣動性能使用。
並列摘要
Wind turbines play a vital role in infrastructures to satisfy the promise of Net Zero Emissions. Compared to horizontal axis wind turbines (HAWT), vertical axis wind turbines (VAWT) are considered to be the more versatile option. One of the major disadvantages of VAWT is the relatively weak power output; therefore, there is still on strong demand to increase its efficiency. This thesis combines swept blades with the concept of sweep startup position. It aims to investigate the relationship between sweep startup position ratio (α) and sweep offset distance (ΔV) and to shed light on the underlying phenomenon. The VAWT of interest is an H-Darrieus type with 3 blades. It is driven by NACA 0021 airfoils, and has a rotor diameter and wingspan of 1.03 m and 1.456 m, respectively. The study is conducted numerically with ANSYS Fluent commercial software. The k−ω SST turbulence model was chosen for its superior resolution on complex turbulent flows with boundary layers. The numerical simulation was first validated against prior studies. Mesh independence test follows to achieve the balance between quality mesh and swift computation time. It is found that backward-swept blades can generally produce more torque in every situation, with ΔV=+0.2c performing exceptionally when α=0.25~0.75. While ΔV=+0.2c and ΔV=+0.6c blades have very similar power coefficients when α=1.00. Forward-swept blades, on the contrary, perform comparatively worse. On close examination of various contour and streamline figures, it is observed that forward-swept blades experience severe dynamic stalling at upwind regions. This phenomenon is exaggerated with the increase of sweep offset distance. Therefore, it is concluded that backward swept blades with small sweep offset distances are preferred to increase the performance of H-Darrieus VAWT with U-shaped swept blades.