本實驗目的在探討彎管二次流所造成之動量混合效應，吾人欲瞭解在不同彎管入口流場條件下，彎管出口下游區域流場特性之變化，因此在彎管入口，除了以完全發展管流流場為實驗條件外，另外又進行非軸對稱的速度分佈作為彎管入口條件，其方法為在彎管上游入口加裝一柱狀體破壞完全發展流況。本實驗將對此兩種不同入口流況，進行彎管下游流場速度及紊流擾動的量測並作分析比較。

　　彎管入口為完全發展流況，出口段軸向速度分佈扭曲，渦流為一順時針大尺度與中心兩小尺度結構，0~15D軸向最高速區域旋轉了約 ，軸向、徑向與漩向紊流衰退率分別為42.1﹪、23﹪與28.6﹪，紊流雷諾應力擾動項 造成軸向速度高低區域分佈不均(偏心)； 項使最高軸向速度旋轉且分佈面積擴散(均勻)。

　　彎管入口為非完全發展流況，出口段軸向速度分佈較對稱，渦流為單一順時針結構，0~15D軸向最高速區域旋轉了約 ，紊流擾動與紊流雷諾應力造成的影響與彎管入口為完全發展流況相近似。
　
　　本實驗中，彎管下游15D處，軸向速度分佈最均勻，彎管入口流況改變對下游軸向速度分佈是否均勻，影響並不大。

　　The present study is to investigate the phenomena of momentum mixing in a pipe flow downstream of two elbows out-of-plane. Two different upstream conditions were applied to the entrance of the elbows, i.e., fully-developed flow condition and non-fully developed flow condition. During the experiments, distributions of mean flow velocity, turbulent intensity and Reynolds stress were measured at a Reynolds number of . The experimental results for the two cases were studied and compared as below.
　
　　With fully developed pipe flow upstream of elbows entrance, the axial velocity distribution downstream of the elbows is characterized by three secondary flow cells. The large one is situated near the wall (clockwise) and the two smaller ones are near the center. As flow convecting to 15D downstream of the exit of elbows, the cell with highest streamwise rotates about . Decaying rates of turbulence intensities in axial, radial and tangent directions are 42.1﹪, 23﹪and 28.6﹪.The turbulent Reynolds stress, is closely linked with the non-uniform distribution of axial velocity in the radial direction, and is associated with the rotation of secondary cells and make the axial velocity distribution more uniform.

　　With non-fully developed flow upstream of elbows entrance, the axial velocity distribution downstream of the exit of the elbows appears to be more symmetrical. The turbulent intensity and turbulent Reynolds stress show the same effects as with the fully developed upstream of the elbows.
　　
　　In this experiment, axial velocity distribution appears to be uniform at 15D downstream of elbow exit and is insensitive to the velocity distribution upstream of elbows.

中文摘要……………………………………Ⅰ
英文摘要……………………………………Ⅱ
誌謝…………………………………………Ⅳ
目錄…………………………………………Ⅴ
圖目錄………………………………………Ⅶ
符號說明……………………………………ⅩⅥ

第一章簡介..........................1
1-1前言.............................1
1-2文獻回顧.........................2
1-3研究目的.........................3

第二章實驗設備與模型................5
2-1完全發展管流設備.................5
2-2皮托管...........................5
2-3壓力轉換器.......................5
2-4兩不同平面彎管組合設備...........6
2-5熱線測速儀(hot-wire anemometer) .6
2-6資料收集系統.....................8

第三章實驗步驟與方法................9
3-1實驗條件.........................9
3-2參數分析........................10
3-3理論分析........................11
3-4入口條件改變....................12
3-5直管完全發展管流之位置..........13

第四章實驗結果與討論...............15
4-1直管完全發展管流之位置確認......15
4-1-1直管速度分佈校驗..............15
4-1-2壓力梯度量測..................15
4-2兩不同平面彎管下游速度分佈......16
4-2-1入口條件為完全發展管流的情況...16
4-2-2入口條件為有T形鈍形體干擾的情況...19
4-3紊流強度分析........................22
4-3-1入口條件為完全發展管流的情況......22
4-3-2入口條件為有T形鈍形體干擾的情況...24
4-4紊流雷諾應力分析....................25

第五章結論.............................28

第六章參考文獻.........................30

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