本文以數值方法模擬垂直軸風力發電機(vertical-axis wind turbines,VAWT)單一翼片(NACA0015)在二維及非穩態流場中動態失速之行為，模擬結果將與實驗現有之速度場與渦度場作驗證，輔以壓力場及升力係數作分析，此外，本研究將引入拉格朗日連結結構(Lagrangian Coherent Structures, LCS)之概念，以拉格朗日的觀點以及根據不同質點的軌跡來進行分析，此方法可有效的評估流場結構並且補抓一些傳統的尤拉(Eulerian)觀測法所無法描述的現象，而本研究將運用拉格朗日連結結構來分析由模擬所得到擺動翼片之動態行為，並運用質點(群)追蹤技術來協助分析較為複雜的流場結構。
模擬結果在定性上可有效地捕捉此動態流場結構，而分析範圍則是以翼片第一次升力下降的過程為主。依本研究之分析結果可證實，由翼片前緣剝離之順時針低壓渦漩為影響動態失速之主要原因，當此順時針渦漩剝離並接近翼片尾端時，將引發另一尾端逆時針低壓渦漩，而此逆時針渦漩將會影響翼片下表面流體，並分別將流體吸引至翼片上表面或尾部逆時針渦漩中，直至所有渦漩完全剝離翼片，此動態行為才會完整結束，而升力從此刻起又會重新升高。除此之外，本模擬藉由觀察翼片下表面的拉格朗日連結結構，發現此結構與翼片前緣渦漩所導致的失速延遲有相互關聯，此分析結果也顯示拉格朗日連結結構分析法與尤拉方法的相輔相成可以協助本研究深入瞭解動態失速的複雜流場結構。

This research focus on the dynamic stall about a single airfoil of vertical-axis wind turbines (VAWT) on 2D and unsteady flows by numerical simulation. The simulation has been validated by velocity and vorticity measurements of the experimental data, and analyze with lift coefficient and pressure contours. Besides, this simulation tries to use the concept of Lagrangian Coherent Structures (LCS) and different particle tracks to analyze. This method can evaluate structures of flows effectively, and capture some phenomenon which traditional Eulerian method cannot describe. Furthermore, this research use Lagrangian Coherent Structures to analyze the result of simulation on a pitching airfoil, and use the particle(s) track technics to illustrate more complicated flow structures.
The result of simulation can capture the dynamic flows effectively on qualitative, and the range of analysis focuses on the first time of decreasing lift coefficient on airfoil. According to the result, the leading edge vortex is the main reason effecting dynamic stall. As the leading edge vortex sheds and is close to the trailing edge, it will cause a trailing edge counterclockwise vortex. This vortex will affect the fluid under airfoils, and the fluid will be attracted to upper airfoil or trailing edge counterclockwise vortex. Until all of vortexes shed from the airfoil, this phenomenon finished, and from this time the lift coefficient will rise again. Besides, the simulation have observed the LCS on the lower surface of the foil can be related to the delay of stall due to the leading edge vortex. The result shows that LCS analysis together with other Eulerian method can help this research to have better understandings of the complexity of the dynamic stall.

目錄
中文摘要 i
Abstract ii
目錄 iii
圖目錄 iv
符號說明 v
第一章 緒論 1
1.1 前言 1
1.2 文獻回顧 2
1.2.1 動態失速 2
1.2.2 紊流模型 3
1.2.3 拉格朗日連結結構 5
1.3 研究目的 6
第二章 研究方法 7
2.1 模擬擺動翼片之數值方法與流程 7
2.1.1 流體統御方程式 7
2.1.2 翼片運動方程式 9
2.1.3 流場幾何、邊界條件及網格設定 11
2.2 拉格朗日結結構： 13
第三章 結果與討論 21
3.1 模擬與實驗之驗證 21
3.2 動態失速之驗證與分析 22
3.3 拉格朗日連結結構分析法 23
3.3.1 驗證拉格朗日連結結構劃分不同動態行為之能力 24
3.3.2 以拉格朗日連結結構分析擺動翼片之動態失速 25
第四章 結論與建議 29
參考文獻 51

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