可調仰角葉片應用於垂直軸風力機性能提升之研究

Application of Variable Blade Pitch Control on Improving the Performance of Vertical Axis Wind Turbine

蘇信彰(Sin-Jhang Su)

指導教授 ： 鄭仁杰

國立虎尾科技大學/工程學院/航空與電子科技研究所/碩士(2012年)

https://doi.org/10.6827/NFU.2012.00062

摘要

垂直軸風力機具有較水平軸風力機不受風向轉變影響、架設容易與噪音小等優點，且可安裝於市區、市郊的建築使用，在提倡綠色能源於住宅生活的前提下，垂直軸式風力機成為極具發展潛力的項目。本文以數值模擬方式探討垂直軸風機葉片的氣動力學現象，深入瞭解風力機葉片的動態空氣動力流場特性，藉此設計規劃葉片仰角的控制方法，以達成提升性能的目標。
本文首先探討單葉片風機的非定常空氣動力特性，選用NACA 0015翼剖面及弦長為9cm葉片，風力機旋轉半徑為45 cm，自由流風速為7m/s及尖速比為2.5的條件下，分析葉片切線力係數隨風機轉動幅角變化的原因，以了解葉片在轉動的過程中，其流場對氣動力性能的影響。並依據流場分析結果，設計多型固定式葉片俯仰角與可調俯仰角葉片的葉片仰角的控制模式。結果顯示，葉片仰角的改變對垂直風機流場結構有明顯的影響，藉由葉片臨界失速時減小葉片的攻角，可以有效降低負轉矩的區域。在所有探討的模式中，最高可以提升平均切線推力係數達8.18％。
本文接著進行三葉片垂直風力機氣動力性能特性探討，首先分析風機葉片設計參數對性能的影響，設計的參數包括葉片的厚度，葉片的弦長與葉片弧度的影響；並依據單葉片風機分析結果規劃多種固定式葉片俯仰角與可調俯仰角葉片控制模式以提高風機之效能。結果顯示，在適當的葉片厚度時，能提高低尖速比時的平均扭力係數；在翼片弧度的影響部分，結果顯示有弧度的葉片會降低其最大平均扭力係數，但是具有適當弧度的葉片則有利於風機的自我啟動；在翼片弦長影響的部分，當葉片的弦長越長時，其平均扭力係數會越低，但平均扭力則呈增加趨勢，且會讓最大平均扭力發生的位置往低尖速比移動。在仰角控制方面，結果顯示，仰角規劃模式與翼尖速度比有關，適當的葉片仰角模式，能夠有效降低負轉矩區域，減少風力機的振動，並且能夠提升平均扭力係數進而增加風能擷取效率，提高風力機的發電效率。固定仰角部分在所有探討的模式中，最高可以提升平均扭力係數達243.16％。可變仰角部分在所有探討的模式中，最高可以提升平均扭力係數達486.06％。

關鍵字

垂直軸風力機 ； 葉片仰角控制 ； 非穩態空氣動力流場 ； 動態失速 ； 數值模擬

並列摘要

In viewing that the Vertical Axis Wind Turbines (VAWT) have the advantages over the Horizontal Axis Wind Turbine (HAWT) in insensitive to changing wind directions, low noise and easy installation for buildings in urban and suburban areas, they are being favorably considered for current and future green living environment. On the other hand, the VAWTs are suffered from the inherent problems of no self-start, lower efficiency compared to HAWT, and structural vibration. These problems enlighten that more research efforts are needed, in order to improve the performance of the current commercial VAWT products. This study is intended to improve the performance a VAWT by controlling the pitch angles of the turbine blades while rotating.
A single blade wind turbine simulation is performed firstly to investigate the unsteady aerodynamic characteristics and the relation between the tangent force corresponded to rotating angle. The NACA 0015 airfoil is chosen as the section of the rotor blade with chord length 9cm and the radius of the wind turbine is 45cm. The wind speed and tip speed ratio are 7m/s and 2.5. Several fixed and variable pitch angle models are applied to investigate the unsteady flow field of the wind turbine by the methods of computation fluid dynamics. Results show that these blade pitch control models reduced effectively the negative torque regime as well as increase the tangent force of the turbine blade about 8.18% comparing with the without pitch control model.
A three blades model is proceeded to study the aerodynamic characteristics of the vertical axis wind turbine. The effects of turbine performance are carried out with varying design parameters including thickness, chord length and camber. Results show that, the average torque coefficient is increased at lower tip speed ratio for the blades of proper thickness. The camber airfoils have the potential to self-start; however, the average torque coefficient shows a reduction in peak efficiencies. The longer the chord length of the blade, the average torque coefficient is reduced. However the average torque is increased. And the point of maximum average torque occurs at lower tip speed ratio. For the pitch control consideration, the models of pitch control are related to tip speed ratio. An appropriate pitch control model can effectively decrease the range of negative torque and the vibration of the wind turbine. The average torque coefficient as well as the energy capture efficiency can be improved. Therefore, the efficiency of the wind turbines in power generation will be enhanced. The efficiency can be raised 243.16% with fixed pitch control. And the efficiency can be enhanced to 486.06% with variable pitch control.

並列關鍵字

VAWT ； blade pitch control ； unsteady aerodynamics ； dynamic stall ； numerical simulation

參考文獻

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