波動薄層流輸沙與紊流特性之研究

Abstract

本文應用紊流模式解析薄層流（sheet flow）瞬時輸沙濃度分佈、流速剖面與摩 擦係數等邊界層物理量，進而探討平均輸沙量與影響因素之關係。計算結果顯示，瞬時輸沙 濃度之阻尼使流速剖面較無濃度情況缺損現象更為明顯；紊流動能（ kinetic energy ）及 渦動滯度（ eddy viscosity ）亦隨濃度之增加而變大； 平均輸沙量約與最大徐爾滋數（ maximum Shields number ）的 4.19 次方成正比關係。 本文紊流模式之計算結果亦與試驗 數據比較，結果顯示預測值與實測值呈合理之一致性。A numerical model describing the characteristics of sediment transport rate and turbulence under waveinduced sheet flow conditions is presented. The interaction of the fluid and sediment is simulated. This model predicts the instantaneous sediment concentration and the physical quantities of the moving boundary layer over sea bed. Computational results show that the presence of suspended sediments retards flow velocity and increases velocity defect. The turbulent kinetic energy and eddy viscosity increase with the increase of sediment concentration. The mean sediment transport rate is in terms of the maximum Shields number based on the calculations of velocity profile and sediment concentration. Comparisons between numerical results and laboratory observations are made and favorable agreements are found.