縱向二次流之流動機制，不只具有傳輸作用，其下降流掏刷底床形成砂谷( trough )，而被刷起之細粒料物質，藉由上昇流之撥掃帶動，形成砂脊( ridge )，此三維結構物稱為砂帶( sand stripe )。吾人依據此一天然現象，在實驗室明渠水槽中，於玻璃底床黏貼3×3平方釐米之正方形結構物，以三維光纖雷射杜卜勒流速儀( 3-D FLDV )觀察加糙物對橫向流場所造成之影響，及其水力特性。
實驗條件同為粗糙底床與0.1%渠坡，寬深比分為2與4；福祿數分別為0.73及0.78；流場雷諾數則為50800與38375。量測之項目涵蓋底床剪應力、渦度、紊流強度及雷諾應力等物理性質，並與洪(2003)之光滑底床實驗結果進行比較。
粗糙底床流場中之二次流之各項物理性質與光滑流場有所不同，在凸起物( ridge )附近尤為明顯，底床加糙對橫向流場之作用呈現窄而深之影響。加糙物相對於水深之比例，為影響底床剪應力分佈重要因素之一，而欲觀察底床剪應力分佈型態，可藉由分析雷諾剪應力等值圖而得。
直線渠道之二次流通常受紊流非等向性影響，生成於角隅區或近邊界區。二次流所具傳輸之功能，會運移物質、動量及熱能，在流場中建構出速度、溫度以及物質濃度之三維結構性。二次流之流速，相對於主流向最大流速而言，其比例甚小(約5%)，卻能深深地影響這些物理現象。

Secondary currents not only transport heat, energy, mass, and pollution, but also cause the structures of downstream river by interaction with river bed. Sand stripe, which includes trough and ridge, is a 3-D complex structure that may exist in a river. A trough is formed by the downward flow of the secondary current, and the ridge is caused by the upward flow.
In this study, experimental investigations are performed in a straight open channel with rough bed (two rough stripes) and fully developed turbulent flow to increase our understanding of the flow structures. The channel width and slope are 25 cm and 0.1%, respectively, and the aspect ratios are 2 and 4. The results are compared with Hong’s (2003) smooth bed experiments.
In contrast to the smooth bed experiments, the major difference occurs around the ridge. The bulge structures have significant effect on the transverse flow. The relative roughness (roughness height over flow depth) influences the transverse distribution of the boundary shear stress, which can be observed by analyzing the plot of iso-Reynolds’ stress curves.
Secondary currents in a straight open channel are induced by the isotropic property of turbulent flow, and frequently occur near the corners or channel boundaries. Although the velocity of the secondary currents is usually very small (less than about 5%) as compared to the maximum velocity in the longitudinal direction, it has significant effect on the 3-D structures of the velocity, temperature and concentration of material in the flow.

中文摘要 I
Abstract II
目錄 III
圖目錄 VI
表目錄 IX
符號說明 X
第一章 緒論 1
1-1.前言 1
1-2.研究目的 2
1-3.內文組織 2
第二章?文獻回顧 3
2-1二次流 3
2-1.1簡介 3
2-1.2二次流討論 7
2-2邊界剪應力 11
2-2.1邊界剪應力之量測 11
2-2.2邊界剪應力分佈 12
2-2.3 壁定理 14
2-3紊流強度 18
2-4雷諾剪應力 20
第三章 三維實驗設備與量測 23
3-1實驗設備 23
3-1.1循環水槽 23
3-1.2三維FLDV系統 27
3-2 實驗設計及佈置 30
3-3 正式實驗 43
第四章 三維量測結果與分析 46
4-1平均速度 47
4-2 二次流 53
4-3 底床剪應力 57
4-4.紊流特性探討 60
4-4-1渦度 60
4-4-2紊流強度 64
4-4-3紊流非等向性 69
4-4-4雷諾剪應力 71
4-5渦度方程式之分析 75
第五章 結論與建議 84
5-1結論 84
5-2建議 89
參考文獻 90
附錄 93

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