二維彎道水理模式之研究

Abstract

本研究旨在用數值模式探討水流流經彎道時,其水理之特性與二次流強度 之發展情形.所採用的模式為深度平均二維淺水波水理模式 ,並採用正交 曲線座標係統,以適應複雜的幾何邊界,使其能應用至不規則渠道.參考前 人之分析,模式中二次流之影響乃由一側方向平均速度再加上一三角對稱 流速剖面所組合而成.並將模式運算結果與 de Vriend(1977) 之兩組實驗 數據及 Yeh(1990) 之動量矩模式作比較,以驗證模式之可靠度.由結果可 看出本模式在凹岸之模擬已能將流速拉高而與實驗值相近;在凸岸之模擬 則尚無法完全有效地使流速降至平均值以下,其二次流強度亦未能有效的 顯現.其原因可能在於水深平均二維模式尚無法完全有效地引進二次流對 流之效應 .但總括來說,本模式之模擬結果與實驗值的比對在趨勢上已趨 於一致,與動量矩模式之結果也極為相近,在實際應用上當有其可靠性. A two-dimensional depth-averaged model is developed here to simulate the flow pattern and the development of secondary flow strength as flow passes through the bend. The depth-averaged model is developed on the basis of the orthogonal coordinate system to be adapted to the complex geometric boundary and the irregular channels. The influence of secondary flow strength is taken into account on the transverse mean velocity by adding an angular velocity profile. The simulated results are compared with sets of experimental data conducted by de Vriend(1977) and the results from Yeh's moment model(1990) to show the reliablity of the newly-developed model. By viewing the comparsion results, it can be seen that the longitudinal velocity along the concave bend has been increased due to the secondary flow effect and close to the experimental data. However, the secondary flow effect on the velocity along the convex bend is insignificant. The insignificant effect of secondary flow along the convex bend may be attributed to that the depth-averaged model can not effectively introduce the advective influence of the secondary flow in the simulation. Neverthless, the simulated results have the consistent trend with the experimental data and the results from the Yeh's moment model. It is expected that this model should be reliable for the practical use.