| 摘要: | 垂直軸風力機(vertical axis wind turbine)葉片的非定常空氣動力受到複雜流體行為主導，主要是來自隨著旋轉角度變化的相對攻角，誘發渦流和尾流的產生以及紊流尾流間的交互作用。此外，支撐支撐臂亦會干擾風的流動，並造成與風力機轉動方向相反的力矩，影響葉片的受力特性以及風力機效能，目前這方面的研究仍相對缺乏。 本研究以計算流體力學軟體FLUENT模擬10 kW斜式旋翼垂直軸風力機的三維氣動力特性，模擬外型除主葉片外，亦將支撐臂、塔架納入考慮，以檢視在風速為2~12 m/s、尖端速度比為1~4，葉片的推力變化，輔以模擬視流分析動態失速前後，渦流溢放的特性以及對推力的影響。此外，另一項重點在於分析支撐臂修正影響、幾何外型有無支撐臂和塔架等因素對葉片受力、功率特性的影響，並歸納各風速下合適的操作轉速。研究結果顯示出幾何外型有無支撐臂和塔架對葉片推力、風力機功率特性造成明顯的差異，當風速為6 m/s，僅含主翼的功率係數最大值(Cp,max=0.239)發生於尖端速度比為3，主翼、支撐臂、塔架功率係數最大值(Cp,max=0.304)發生於尖端速度比為2，淨值較僅含主翼提昇6.5%。在支撐臂修正影響方面，支撐臂導致的反向力矩在較高尖端速度比時(λ=3、4)，於各風速下皆會明顯降低功率係數。以功率係數大於0.25為基準，歸納風力機在各風速下適合的操作轉速，其中當風速介於2~4 m/s，建議轉速應控制在尖端速度比為2，當風速介於6~ 12 m/s，建議轉速應控制在尖端速度比為2~3的範圍內。 The vertical axis wind turbine (VAWT) has an inherent unsteady aerodynamic behavior due to the variance of angle of attack with the revolutionary angle, causing the generation of the turbulence wake and the wake interaction between blades. In addition, the support arm will also disturb wind flow motion, generating counter torque when the blades are rotating, affecting the characteristic of blade loading and the performance of VAWT. To date, few studies have done in these area. This research uses computational fluid dynamics software FLUENT to simulate the three-dimensional aerodynamics flow of a 10 kW slant-H-rotor VAWT, which has the unique design of curve blades. The effect of support arm and tower is also considered. Solution of three-dimensional flow is obtained to study thrust of blades, the development of vortex shedding when dynamic stall occurs under incoming velocity is from 2 to 12 m/s with various tip speed ratio (1-4). Another key point of the study is to investigate the effect of arm correction, the geometry with/without arm on blade loading and on the performance of VAWT. Finally, the appropriate operation condition under various wind velocity for slant-H-rotor VAWT are summarized. The simulation result indicates the geometry with/without arm make huge difference on blade loading and the performance of VAWT, the maximum power coefficient (Cp,max) is 0.239 at tip speed ratio of 3 for geometry with blade-only, while Cp,max is 0.304 at tip speed ratio of 2 for geometry with blade, arm and tower. For the effect of arm correction, result shows counter torque causing by arm reduces the power coefficient significantly under tip speed ratio is 3 and 4 with various wind velocity. In terms of power coefficient higher than 0.25, the appropriate operation condition for slant-H-rotor VAWT are summarized. When wind velocity is 2 to 4 m/s, the appropriate tip speed ratio is 2, while wind velocity is 6 to 12 m/s, the appropriate tip speed ratio is 2 to 3. |
