旋轉垂直軸風力發電機葉片之撓曲與扭轉之三自由度線性振動分析

Three-degree-of-freedom system of linear vibration of blade bending and fluttering of vertical axis wind turbines

吳運鵬(Yun-Peng Wu)

指導教授 ： 張建成

共同指導教授 ： 郭志禹(Chih-Yu Kuo)

國立臺灣大學/工學院/應用力學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02129

摘要

垂直軸風力發電機相較於水平軸風力發電機而言，具有無風向限制以及噪音較小等優點。風機葉片的振動行為可看作一樑振動的問題，其中樑端點為何種支撐方式，對其振動行為的影響相當大。本研究從能量法的漢彌爾頓定理出發，推導出葉片撓曲-扭轉三自由度之耦合振動控制方程式，其中使三個自由度互相耦合的關鍵參數在於葉片重心以及剪力中心之間的距離 ，而當葉片截面積呈對稱形狀時，該參數的值為零，也就是三個自由度之間將互不耦合。本研究以NACA0015型號之小尺度葉片為對象建立模型，該型號葉片形狀並非對稱，故計算時可以保留三自由度間的耦合特性。以有限差分法將葉片空間及控制方程式作離散，分別對簡支撐和固定支撐兩種邊界求解。再使用工程軟體ANSYS Workbench來做模擬，對葉片作模態分析，得到自然頻率以及模態形狀之模擬值，並與理論值作比較。兩種方法得到的結果，在低頻模態時相當吻合。故以本研究之方法，可以準確地得知葉片的低頻共振自然頻率，如此在設計葉片時，可以透過改變幾個影響較大的變數，避免因風力發電機運轉時產生的振動與葉片發生共振，而破壞葉片結構。
本研究也用實體之小型葉片作模態測試，希望能夠將實驗值與理論值作一比較探討，但礙於實驗設備的不足，模態測試實驗的邊界條件無法與模擬的邊界條件吻合，故最後僅發展出一套實驗流程，沒有可以與理論比較的數據

關鍵字

垂直軸風力發電機 ； 葉片振動 ； 自然頻率 ； 模態測試

並列摘要

Compared to horizontal axis wind turbines, vertical axis wind turbines have the benefit of operation that is independent of the wind direction, lower wind speed to start operation, and less noise. The vibration of blade can be regarded as vibration of a beam. How to support the ends of the beam affect the vibration very much. In this present paper, we start from the energy method of Hamilton’s principle, derive the dynamic governing equations for the blade, which has three degree of freedom (includes bending and fluttering). The key variable to keep the three degree of freedom coupled is the distance from center of gravity to shear center, . When the cross-section of blade is symmetrical, the value of is zero, which means the three degree of freedom will decouple. We creat the model of NACA0015 small size blade. The NACA series blades are asymmetric, so we can keep the three degree of freedom coupled in calculation. We discrete the space and governing equation by finite difference method, solve the cases of simply support and fixed support, respectively. Then use ANSYS Workbench to do the modal analysis. Thus we obtain the natural frequency and mode shape of theory and simulation, respectively. The two results are similar in low frequency mode. By the way we use in this study, we can vary the natural frequency while design the blade, avoiding resonance in operation.
Otherwise, we also do the modal testing of small size NACA0015, expect to compare the result of experiment and simulation. Due to the lack of experimental equipment, the boundary conditions of the modal testing can not coincide with the simulation. Finally we build an experiment process only, without data to compare with simulation.

並列關鍵字

Vertical axis wind turbines ； Blade vibration ； Natural frequencies ； Modal test

參考文獻

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