螺旋式垂直軸風力機的氣動力模擬; Aerodynamics Simulation for the Spiral-H-Rotor Vertical Axis Wind Turbine

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Title:	螺旋式垂直軸風力機的氣動力模擬;Aerodynamics Simulation for the Spiral-H-Rotor Vertical Axis Wind Turbine
Authors:	張智堯;Chih-yao Chang
Contributors:	機械工程研究所
Keywords:	螺旋式風力機;三維氣動力分析;垂直軸風力機;翼尖小翼;計算流體力學;Winglet;Vertical axis wind turbine;Three-dimensional aerodynamics analysis;Spiral-H-rotor;Computational fluid dynamics
Date:	2011-07-12
Issue Date:	2012-01-05 12:28:49 (UTC+8)
Abstract:	本數值研究採用計算軟體FLUENT分析螺旋式垂直軸風力機(10 kW與50 kW)葉片做氣動力分析，由於葉片外型特殊，必須利用三維數值模擬才可得知其複雜的氣動力型態。包括兩項分析工作：(1)探討葉片氣動力特性，包含尖端速度比與不同的入口風速的螺旋式垂直軸風機的輸出功率係數；(2)分析推力係數與方位角的關係，並呈現風機之局部速度、壓力與渦度的分佈，以辨識這些變數對於風機推力的影響。預測顯示當葉片經過轉子中心區之低速區或是渦度梯度變化大之區域皆會大幅降低葉片的推力。此外10 kW風力機預測之最大功率係數（0.356）已相當接近水平軸風機之效率，因此建議風力機操作應在TSR=2~3以保有最大功率。此外，本研究也針對中型螺旋式風力機（50 kW）之葉片做分析，50 kW風力機外形是依據10 kW風力機葉片，為了減少葉片尖端渦流的影響，加入翼尖小翼（如同飛機固定翼之翼尖小翼）的設計與主葉片為垂直安裝，以達提升性能之目的。模擬顯示此風力機最大功率係數接近0.4，但隨風速增加則功率係數曲線下降。模擬結果可知翼尖小翼可增加葉片尖端之高壓與低壓區域，使葉片的壓力差增加，且可降低轉子區後半圓之渦度梯度變化，並提升葉片的有效推力以及最大功率係數。此項氣動力結果可提供螺旋式垂直軸風力機葉片的設計。 This numerical study uses computational software FLUENT to analyze aerodynamics characteristic of vertical axis wind turbines (VAWT) with spiral-H-rotor (two capacities: 10 kW and 50 kW). Because of the unique blade shape, three-dimensional numerical simulations must be utilized for understanding the complex aerodynamic pattern. Two analysis are investigated: (1) study the aerodynamic of blade, including various combination of tip speed ratio and inflow wind velocity for this VAWT, in order to realize the characteristic of wind turbines; (2) analyze the relation between thrust coefficient at different azimuthal angle, and display the distribution of local velocity, pressure and vorticity to identify these variables influence on thrust. Results show that when the blades pass through the area of low speed in the center of the rotor or the area of large variation of vorticity, the thrust of blades decrease significantly. In addition, the predicted power coefficient of 10 kW wind turbine (0.356) is close to the value of horizontal axis wind turbine, and the tip speed ratio is recommended to operate around two to three to have maximum power performance. Another analysis is made for a new blade design of 50 kW wind turbine, which is enlarged from the shape of 10 kW with a winglet attached on the blade tip. The winglet arrangement (similar as it on the fixed wing layout) can reduce the tip vortex strength so that to enhance the power output of wind turbine. Predicted maximum power coefficient close to 0.4 and this value decreases as the incoming wind speed decreases. Simulation shows the blade wih winglet increase both the high and low pressure zone near the blade tip, and thus the amount of pressure difference is enlarged. In addition, the strength of vorticity gradient also reduces in the back rotating circular region. This study can provide useful aerodynamic data for the design of new spiral-H-rotor VAWT.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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