- 學位論文
垂直風力發電機之模擬與扭力及效率分析
Analyzing Aerodynamics of Vertical Axis Wind Turbines with Different Models
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、齒輪箱置於底座方便作業等優點，因此近年來其成為離岸式風機發展的重點對象，垂直軸風力發電機葉片的空氣動力特性是由複雜的流體與風機葉片之交互作用所主導，葉片受到空氣動力所產生的受力情形主要是隨著旋轉角度變化的相對攻角、雷諾數與速度所造成，屬於暫態的周期性問題，本研究是計算大型風力發電機在穩定轉速下之功率輸出與扭力，應用葉片元素理論以擬定常的方式計算受力情形，數值計算的部分是以ANSYS FLUENT計算流體力學軟體以控制方程式Navier- Stokes方程式來計算紊流場下的受力情形，所使用的紊流場模型為K-epsilon。 本研究針對不同尖端速度比(tsr=3、4、5、6)、葉片數(2、3、4)對風機的功率輸出造成的影響進行探討，並以疏密比(1/30、1/45、1/60)來探討葉片元素理論的適用性。發現尖端速度比等於4時有最大的輸出效率，由動力效應以及黏滯效應共同主導，屬於過度區域，在此區域具有良好的效率；葉片數三葉的風機有最佳的效率，四葉風機則是因為會受到前一葉片產生的干擾使得效率降低；因此葉片元素理論在疏密比小於1/45時數值計算與葉片元素理論的結果相當符合，十分適合運用於大型風機的計算，在大於1/45時則葉片元素理論的結果與數值計算有較大的誤差，需使用數值計算的方式才能達到較準確的結果。
並列摘要
VAWTs have the advantages of wind direction with no restrictions and convenient operation .VAWTs become the focus of development of offshore turbines in recent years. The aerodynamic characteristics of vertical axis wind turbines are determined by the complex interactions between the flow and the turbine blades. The complication mainly arises from the change of angle of attack, and Reynolds number of the blade airfoil during rotation and this leads to transient periodic aerodynamic forces on the blade. In this study, we analyze the torque and power output of large-scale wind turbines by using both BEM (Blade Element Method) and numerical method. The parameters of calculations include tip-speed ratio(tsr=3,4,5,6), number of blades(2,3,4), and solidity ratio(1/30、1/45、1/60). We found that the maximum power can be obtained at tsr=4, which is dominated by dynamic effect and viscous effect. The turbine with three leaves have the best power efficiency. When solidity is smaller than 1/45, the results of CFD and BEM are similar. Therefore, BEM is appropriate for prediction of large-scale VAWT.