階梯河道水流型態模擬與阻力分析

Flow Pattern Simulation and Resistance Analysis in Step Channels

10.29417/JCSWC.201206_43(2).0001

陳怡良(Yi-Liang Chen)；李光敦(Kwan-Tun Lee)

階梯－深潭 ； 溢濺阻力 ； 三維流體動力數值模式 ； 舌流 ； 滑移流 ； Step-pool ； spill resistance ； 3D fluid dynamic numerical model ； nappe flow ； skimming flow

中華水土保持學報

43卷2期（2012 / 06 / 01）

97 - 108

繁體中文

水流於階梯－深潭河道流動過程中，產生跌落、翻滾及水躍等水力特性，此三種連續流動過程構成溢濺阻力，而產生大量能量消散。有鑑於山區階梯－深潭河道之幾何形狀過於複雜，難以進行系統化分析；因此本研究由規則階梯渠道著手，利用三維流體動力數值模式，進行詳細的水流型態與阻力分析。研究結果顯示，當流量較低，水流型態為舌流時，水流產生跌落及水躍特性，使得總糙度係數可達0.1以上；而流量較高時，水流型態為滑移流，水流淹沒階梯，其總糙度係數較舌流情況者為低。然而不論流況為舌流或滑移流，階梯渠道之總糙度係數均較模式所設定之渠道表面糙度為大。本研究於階梯河道檢定所得之階梯水流能量消散與總糙度係數之關係，可供後續於山區陡坡河道進行水利工程設計時，選用糙度係數之參考應用。

When water flows over step-pools, plunging from steps to pools, tumbling and hydraulic jumps will be produced. These three kinds of flows result in spill resistance, which generates significant energy dissipation. Since the geometry of mountain step-pools is complicated for flow structure analysis, a 3D fluid dynamic numerical model was used to analyze energy dissipation and flow resistance in regular step channels. Results show that in cases of low flow, the flow is in a nappe flow condition, and plunges from steps to pools and hydraulic jumps are produced. The total roughness coefficient of the nappe flow can reach 0.1. For cases of high flow, water submerges the steps, resulting in a skimming flow, and the total roughness coefficient is comparatively small. Whether the flow is in a nappe or a skimming flow condition, the total roughness coefficient is higher than the channel surface-roughness coefficient set in the numerical simulations. The relationship between the energy dissipation and the total roughness coefficient investigated in this study can be used as a reference for hydraulic design in steep mountain streams.