彎道效應對縱向延散係數之影響分析研究

Abstract

本研究旨在探討彎道效應對縱向延散係數之影響，根據前人之相關研究，探討影響縱向延散係數正確性之無因次延散係數 (Elder,1959)與 (Liu,1977)差異性後，選擇在不同河川應用上具有變動程度與估算誤差較小之 為基礎，進行彎道效應因子之分析討論。進行分析前，首先檢討流速剖面型態對無因次延散係數之影響，結果發現側向速度剖面影響頗巨，且不確定性甚高，因此分析中忽略流速剖面型態之影響，模擬案例均採用均勻入流型態之入流邊界做進一步模擬分析。敏感度分析結果顯示，二次流強度因子 為影響 之重要參數，且二者呈現正相關趨勢；隨著彎道長度因子 之增加，固定 情況下， 展現漸增之趨勢，直至 附近增加幅度趨於穩定。由二次流重要性分析所得之 關係曲線，說明 之產生即對 值造成影響，且該曲線亦可提供做為彎道縱向延散係數決定之參考。

The purpose of this study is to analyze the bend-flow effect on longitudinal dispersion coefficient. The dimensionless dispersion coefficient (Liu, 1977) is adopted herein because of its relatively small variability for the real case. The examination on the effect of velocity distribution shows that varies with the pattern of velocity profile. Hence the following analysis will omit the influence of velocity pattern to avoid its uncertainty. For the inflow boundary in the bend-flow cases the uniform velocity distribution is assumed. The relationship between and bend-flow effect is investigated through the methods of sensitivity and regression analysis. The results show that the relative strength of secondary current caused by bend-flow effect is significant and direct proportional to . Finally, while relative length of channel bend is increasing, the analysis shows is reaching a stable tendency while approaches towards 0.222. The curve derived in this study can be used for estimating the longitudinal dispersion coefficient in bend-flow case.