具被動式裝置角調整功能風機葉片之失效行為分析

Abstract

現今的小型風機為了在提升發電效率的同時，又能同時兼顧風機葉片之安全性，發展出一種改變葉片裝置角之技術。此技術會使得葉片所受的風力負載有所不同。本文目的在針對裝置角調整功能的風機葉片及機構進行安全性評估。 先經由位移控制實驗，探討葉片在靜態負載下的失效，挫屈、破壞。實驗中分別量測葉片不同位置之應變、翼尖位移、夾頭力量，並使用有限元素分析軟體ANSYS，對葉片變形狀況分別作線性與非線性分析，結果顯示非線性分析較貼近實際情形，以此先驗證葉片模型之正確性。 本研究為配合風力發電系統之煞停機制，設計一套裝置角機構使葉片在200rpm下改變9.2度裝置角。為了解旋轉葉片受力之差異，透過一套無線應變傳輸系統，分別對0度裝置角和加裝裝置角機構之葉片進行葉片蒙皮應變量測。在加裝裝置角機構的情況下，發現理論與實驗有所差異，在考量應變、角度變化、扭矩情況下提出一套修正方法，並驗證其正確性。 修正完葉片之正確受力狀況後，在同風速8m/s下，比較0度和9.2度裝置角對風機葉片破壞係數之影響，發現裝置角對葉片各部分的破壞係數都是大幅的下降。結果顯示在高風速下裝置角對於提升風機葉片之安全性有相當程度的幫助。同時機構也是不會失效的。 另一方面經由風場實驗可得知在零度裝置角下，實驗與理論結果相近，因此以理論為依據，在只考慮單一失效模式的狀況下，得知葉片於風速23m/s發生首層破壞。 本研究之主要貢獻為針對有裝置角情況下提出一套修正葉片受力的方法。透過實驗與分析證明裝置角改變不僅可以提高發電效率，也可以有效的降低葉片的破壞係數。確定零度裝置角的情況下，可以用葉片元素理論來評估葉片受力。

To enhance the efficiency of power generation and the safety of wind blades, a technique for designing a passive pitch angle control mechanism for a small blade was developed. This technique will make the wind load on the blade with pitch control capability different from that of the blade without. The purpose of this paper is to evaluate the safety of the wind blade with pitch control capability. First of all, the test results of a composite wind blade subjected to stroke-control testing are used to validate the finite element model of the blade. We construct the relationship between the force and the tip displacement and study the failure modes such as buckling and material failure of the blade. The finite element analysis program ANSYS is used to analyze the linear and nonlinear deformations of the blade. It has been shown that the nonlinear finite element method can produce more accurate results than the linear one when compared to the experimental results. Secondly, the pitch control mechanism is designed to achieve a pitch angel of 9.2 degree when the rotor speed reaches 200rpm. To understand the differences of wind forces on the blade with and without pitch control, strains on the skin of the rotating blade with/without pitch control capability are measured using a wireless transmission system for wind loads identification. In the case with pitch control mechanism, it has been shown the theoretical and experimental strains are different. A method is proposed to correct the wind load via the minimization of the sum of the squares of the differences of the theoretical and experimental strains. As for the case with 0 degree pitch angle, the experimental and theoretical results are similar. Next, the failure indices based on the Tsai-Wu criterion of the blade with pitch angles of 0 degree and 9.2 degree at wind speed of 8m/s are determined through the finite element analysis of the blade. It has been found that the failure index of the blade with 9.2 degree pitch angle is much lower than that of the case with zero pitch angle. The results show that at high wind speed, pitch control can enhance the safety of the blade and the pitch control mechanism does not fail. On the other hand, with the consideration of only one failure mode, it has been found that the first-ply failure of the blade with 0 degree pitch angle occurs at 23m/s. Finally, the main conclusions of this study are as follows. A method of correcting the force of blade is proposed for the case with pitch angle. Through the experiment and analysis, it has been demonstrated that the change of pitch angle can not only improve the power generation efficiency but also effectively reduce the failure index of the blade. In the case of zero degree pitch angle, the blade element theory can be used to evaluate the blade force.