傳統風力發電機葉片的設計是以“額定風速”做為主要運轉之設計依據。然而設計人員能取得的地區風場資料通常為〝月平均風速〞或〝年平均風速〞,因此就常採取平均風速作為設計葉片之額定風速。在該風速度下,所設計出的風力機葉片具有最高的運轉效率(功率係數,Cp值)。但在現實世界中,風速與風向總是受到季節性或不規律的氣象因素而變動,風力機葉片相對於風的攻角也會隨之改變,使昇力、阻力產生變化,造成風力發電機輸出改變,就不再是在原設計的條件下運轉,也就是一旦實際風速偏離原設計點的風速時,如果下游的負載維持不變,風力發電機的葉片轉速必然會隨之改變。一旦轉速改變,對感應式發電機或同步發電機而言,葉片轉速偏離發電機原設計的同步轉速太多代表發電機的效能會大幅喪失,因此本研究擬研發一種新的簡單方法來實現設計一種“能適用於不同風速下”的葉片幾何形狀,使葉片在不同風速下能具有整體的較佳功率係數。所設計出的葉片再利用計算流體力學(CFD)方法,以商用軟體 Gambit建構網格,Fluent進行流場的解析,以提供該葉片在風速變動下的各種性能數據。
Traditional design of the turbine blade started with a “rated wind speed” which is the wind speed that the turbine is assumed to operated at most of the times, and the turbine blade is supposed to acquire the highest efficiency (power coefficient) at that wind speed. In the real world, wind speed hardly can be kept at a steady value for a period of time but is usually varying within a range from an “averaged value”, which is so called the rated wind speed. Therefore, a good designed blade should be not only has good efficiency at the “rated” wind speed, but also have satisfying efficiency within a range from the rated wind speed. The commercial software Gambit is used to generate the mesh system required, and Fluent is used to solve the flow field around the rotating blade and verify the power coefficient results.