臺灣博碩士論文加值系統

本文主要的目的是以數值分析之控制體積法 (Control Volume Method) 配合 紊流模式及 紊流模式，來模擬二維非平行雙噴口射流 (兩噴口間無連接壁) 在不同的射口偏角 (Deflected Angle， ) 及背景流 (Background Flow) 影響下流場所產生的變化和干涉情形，同時對收斂域、沒入域及合流域之平均流與紊流性狀變化及其它物理現象做進一步的窺探，同時與前人之實驗結果相驗證來比較兩不同模式模擬結果之差異。
數值模擬的項目包括有平均流流速分佈、無因次流速分佈曲線、紊流分量強度及紊流剪應力等。由計算結果與量測資料比較顯示，兩噴口間及其兩外緣必須給與一適當均勻之同向背景流來補充流場的捲增效應，以確保流場穩定性；同時背景流與噴口偏角經迴歸分析，發現存在一三次多項式之關係。沒入點(M.P.)及合流點(C.P.)和無因次偏角 之關係顯示當噴口偏角增大時，兩不同模式模擬之射流沒入點位置隨偏向角皆呈線性函數關係，而合流點則與噴口偏角皆呈二次函數關係；但比較實驗量測值發現 紊流模式所得之結果較 紊流模式更接近實驗結果。當射口偏角為270時，二射流已不再受捲增作用的影響故流動方向是呈直線軌跡直接於噴口方向上相互衝擊沒入、交混與實驗結果吻合，由 紊流模式所得之結果亦較 紊流模式更加可看出此效應。綜合比較實驗與數值之結果可看出平均流流速在合流域內存在相似性，在流場形貌、射流軌跡、平均流特性、紊流正應力與紊流剪應力皆發現有相同的分佈趨勢。整體而言，k-ε紊流模式又較k-ω紊流模式更接近於實驗結果。

The numerical simulation results of the flows of two parallel/inclined planar turbulent jets are presented in this paper. This study adopts the control volume method for simulating the mean quantities of the two-dimensional averaged Navier-Stokes equations associated with and turbulent models. The computational results of these two turbulent models were validated with the experimental investigations and compared each other for the related physical quantities.
The comparison includes mean flow direction, turbulent intensities and Reynolds stress; and demonstrates that (1) background flow is needed for the numerical simulation to reinforce entrainment and ensure the stability of the flow field. There exists a third order polynomial relationship between the background flow and the deflected angles. (2) The relationship of Merged Point (M.P.), Combined Point (C.P.) with dimensionless deflected angle shows that a linear relationship exists between the M.P. and deflected angels. Nevertheless the relationship of C.P. and the deflected angels is a second order polynomial. By comparing the experimental measurements, the numerical results of turbulent model is more closed to experimental results than turbulent model. (3) When the deflected angle increases, vortex center will shift upstream with the increase of the inclined angle of the dual jets in the converged region until 27 degree. Beyond this critical angel (27degree), the vortex profile will not change any more, it agrees well with the experimental result. General comparison of the experimental and numerical results show that the mean velocity profiles approach self-preserving in the combined region, also show that the fluid formal, jet track, mean velocity characteristics, turbulence stresses and turbulence shear stresses all have the same developing trend. Overall, the simulation of k-εturbulent model is much more closed to the experimental measurement than that of the k-ωturbulent model.

中文摘要 I
英文摘要 II
誌謝 IV
目錄 V
表目錄 VII
圖目錄 VIII
符號說明 XII
第一章 導論 1
1-1 前 言 1
1-2 雙噴口射流 1
1-3 紊流模式簡介 3
1-4 文獻回顧 4
1-5 研究動機方法與目的 7
第二章 理論分析 8
2-1 紊流性質 8
2-2 基本假設 8
2-3 控制方程式 8
2-4 k-ε紊流模式 12
2-5 k-ω紊流模式 14
第三章 數值模擬 17
3-1 廣義微分方程式 17
3-2 微分方程式之離散化 18
3-3 速度與壓力修正式 22
3-4 SIMPLEST 法則之計算程序 24
第四章 數值模擬 26
4-1 邊界條件 26
4-2 背景流與內向角之關係 27
4-3 收斂域與沒入域平均流之觀察 28
4-4 收斂域與沒入域紊流性質之觀察 30
4-5 合流域平均流、紊流性質之觀察 31
第五章 結論 33
參考文獻 36

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