中尺度的模擬軟體被廣泛應用在天氣預報和大氣研究的領域，不過在風機架設相關的研究以小尺度模型的解析度較為適當。本研究以計算流體力學(Computational Fluid Dynamics, CFD)分析彰化外海測風塔周圍流場變化，使用中尺度天氣預報模型(Weather Research and Forecasting, WRF)模擬結果作為邊界條件，在WRF缺少的低層以冪次定律(power law)推估，模型中考慮地表粗糙度和紊流濾波器，另外，本研究結合WRF-LES模型與質點追蹤法的邊界型式，預測數分鐘內流場動態行為，最後與量測值比較CFD的模擬結果。
在冪次律邊界條件的模擬，分別使用LES (Large eddy simulation)模型、k-ε (k-epsilon)模型與FBM (Filter-Based Model)進行模擬，模擬結果中各模型在80公尺以上高度風速變化趨勢與WRF相似，在高度50公尺以下LES模型的α值、標準差和相關係數等比k-ε模型接近量測數據。另外當FBM之濾波器尺寸大於10倍網格高度時，FBM模擬結果會與k-ε模型相似，靠近地表的風速由大至小依序為LES、k-ε和FBM模型。質點追蹤法的模擬結果中風速大小接近上游速度而逐漸上升。比較二階質點追蹤法在邊界上風速與一階差異，X和Y方向誤差小於1%，Z方向誤差小於10%。

Mesoscale numerical approach has been applied widely for weather prediction and atmospheric research. Nevertheless, microscale model is more appropriate for siting of wind farms. The objective in this study is to analyze offshore wind field in Changhua by coupling a CFD (Computational Fluid Dynamics) solver and boundary condition provided from WRF (weather research and forecasting) beyond 40 m above sea level. The boundary conditions below 40 m were based on power law wind profile with considerations of the surface roughness and filter function. Furthermore, a particle tracking method for the boundary condition has been developed. Furthermore, all of the CFD results have been compared with the measured values.

The results beyond 80 m show good agreement between WRF and CFD, and the correlation coefficient and power law exponent of LES model below 50 m are better than those values predicted by k-ε model. Besides, the result of FBM is similar to that of k-ε model as the filter size is too large. The predicted velocity near the sea level of LES model is apparently faster than that of k-ε model and FBM. As for the particle tracking method, since its upstream velocity near the boundary is faster, the ensuing predicted velocity overruns that by WRF-LES model. The deficiencies between first and second order particle tracking methods are insignificant, and hence the first order scheme is sufficient.

論文審定書 i
誌謝 ii
中文摘要 iii
Abstract iv
目錄 v
圖目錄 vii
表目錄 ix
符號說明 x
第一章 緒論 2
1.1 前言 2
第二章 文獻回顧 3
2.1 WRF模型 3
2.2 紊流模型 5
2.2.1 k-ε模型 5
2.2.2 LES模型 7
2.2.3 WRF-LES 8
2.3 冪次律(power law)速度分布 10
第三章 研究方法 13
3.1 冪次律邊界風場模擬 15
3.1.1 冪次定律(Power law) 17
3.1.2 Large eddy simulation model 17
3.1.3 Standard k-ε model 18
3.1.4 Filter-Based Model 19
3.1.5 Law of the wall modified for roughness 19
3.2 質點追蹤法 21
第四章 結果與討論 26
4.1 冪次律邊界流場模擬 26
4.1.1 計算指數值α 26
4.1.2 計算域大小測試 29
4.1.3 網格測試 32
4.1.4 LES模型和k-ε模型模擬結果 35
4.1.5 FBM模型模擬結果 41
4.2 質點追蹤法 45
4.2.1 一階質點追蹤法結果 45
4.2.2 二階質點追蹤法 58
第五章 結論與建議 61
參考文獻 63
附錄 69

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