高效率碳纖維束加勁玻璃纖維複合材料風力葉片之研製

Abstract

小型風力發電機的三個重要研發課題是效率、可靠性和成本, 其中風力葉片與這些課題均是息息相關的。葉片是風機的吸能元件, 其效率及可靠性可直接影响風機的發電效率及效益, 目前的葉片在這方面仍有很多尚待改進之處。複合材料具有多項優點, 且因玻璃纖維布的價格較低, 故目前的葉片多用玻璃纖維複合材料來製作。但玻璃纖維布的重量仍嫌稍高, 剛性亦稍嫌不足, 都會影响葉片的靈活性及效率, 故目前的設計方式仍有可改善之處。 本計畫擬採用新的葉片結構設計及利用少量碳纖維紗束加勁玻璃纖維布來研發一2.5m長、可供5kW發電機使用的葉片, 使葉片的效率可以達到0.38以上、重量在6公斤以下及可承受的風速在60m/s以上。本計畫將從設計、製造和測試等三方面研發所提出之新一代葉片: 1. 設計研究 本研究將利用商用空氣動力分析軟體Fluent和Javafoil分析葉片在特定轉速和風速下的升力和阻力係數分布, 然後利用葉片元素法計算葉片的負載。 因葉片的效率與其所產生之扭力成正比, 故用疊代的方式計算葉片的負載及設計葉片的扭角以取得最大扭力。 然後根據葉片的負載設計葉片的結構, 並由有限單元分析結果識別葉片上的應力走向和集中區域。 使用不同層數的玻璃纖維布設計葉片的蒙皮, 另利用少量碳纖維紗束在應力集中或挫屈容易產生的區域加勁玻璃纖維蒙皮, 如此在成本變化不多下可減少玻璃纖維布的用量, 並能增加葉片的強度, 同時使其重量下降。 2. 製造研究 建立葉片中玻璃纖維布蒙皮、肋板及碳纖維紗束加勁條/片的製程, 其中碳纖維紗束的走向和位置由應力分析來決定。另外, 蒙皮之邊緣及中間沿軸向方向設有特殊之卡溝以供上下蒙皮之接合及蒙皮與肋板之接合, 如此蒙皮與蒙皮及蒙皮與肋板之間可結合為一體, 避免產生剝離和開口破裂的失效模態。 3. 測試研究 葉片需有足夠的強度來承受風速60m/s的壓力, 首先模擬風壓分布, 然後進行Whiffle-Tree靜態負載試驗。量測葉片的首層破壞強度及最大負載能力, 並識別葉片的失效模態, 確保設計及製作方式正確。

The three major issues of R&D in wind power are efficiency, reliability and cost which are closely cross-related. The wind blades of a wind power generator are the important element for energy absorption. The efficiency and reliability of the blades, which is still a major problem to be tackled, can directly affect the efficiency and effectiveness of the generator. Composite materials have many advantages to be used in the industry. In particular, due to its relatively low cost, glass fabric has been widely used to make wind blades. Regardless of its many good points, glass fabric is still not light and stiff enough to make wind blades with the properties of high efficiency, reliability, and maneuverability. In this project, a new design of 2.5m long composite wind blade is proposed to achieve the goal of efficiency larger than 0.38, maximum wind speed resistance greater than 60m/s, and weight less than 6 kg. The following procedure will be adopted to achieve the goal: 1. Design of Wind Blade The aerodynamic code Fluent and Javafoil will be used to analyze the wind pressure acting on the wind blade surface and the Blade Element Method to evaluate the wind loads on the blade. An iterative procedure is proposed to determine the twisting angles at different stations of the blade that can produce relatively large torque for the wind turbine. Based on the calculated wind loads, the structure of the blade is designed using glass fabric composite materials. The locations where the important failure modes such as fracture and buckling are likely to occur are identified in the finite element analysis of the blade. To reduce the weight and increase the strength of the blade, carbon yarn stiffeners are then used to reinforce the blade at the critical locations. 2. Fabrication of Wind Blade The blade is composed of upper and lower skins, a span-wise web, carbon yarn stiffeners, and an aluminum connector. The fabrication processes for fabricating the composite parts of the wind blade are established. To ensure the parts of the blade working as an integral body, specially designed grooves along the edges and in the center of the skins are made for binding the web and skin as well as the upper and lower skins together. 3. Testing of Wind Blade The wind load induced by the wind speed of 60m/s is converted to distributed point loads acting along the span of the blade. The blade is then subjected to static strength testing via the Whiffle-tree approach. The load-displacement and load-strain curves are measured to verify the theoretical predictions. The failure modes of the blade are investigated using the measured data. The suitability of the blade design is finally validated by the experimental results.