适用于明渠流及冰盖流的统一泥沙起动流速计算方法初探

Preliminary Study on Calculation Method of Incipient Velocity ofNon-cohesive Sediment in Open Channel Flow and Ice Sheet Flow

冰盖是北方高寒地区河流冬季常见的一种自然现象。冰盖的出现改变了河流的运动状态,由原来的明渠流变为覆盖流。受冰盖糙率影响,垂线流速分布相应变化,进而影响河床泥沙输移。为进一步探讨冰期河床泥沙输移演变规律,基于Einstein假定,采用滚动起动模型,考虑冰盖下糙率变化、黏性淤积物干重度、相对暴露度对泥沙起动的影响,从理论上推导出了适用于冰盖流的泥沙起动流速公式,并与已有试验数据对比,相对误差集中在1%~10%之间;同时,探讨了本文公式对于明渠泥沙起动的适用性,即当冰盖糙率为0时,可视为明渠流泥沙起动流速计算公式,与实验数据对比,相对误差范围为0%~0.86%,亦可满足计算精度要求。

Ice cover is a natural phenomenon commonly observed in winter rivers of northern regions.Its presence alters the river’s motion from turbulent to laminar flow,affecting the vertical velocity distribution due to the roughness of the ice cover and further influencing the sediment transport on riverbed.To investigate the evolution of sediment transport in glacial rivers,a formula for incipient velocity of coarse and fine sediment particles is deduced theoretically suitable for ice-covered flow based on the Einstein assumption by using a rolling starting model.The effects of roughness change under the ice cover,the dry density of viscous sediment,and the relative exposure degree on sediment incipient motion are considered.Comparison with existing experimental data manifests that the relative error of the proposed formula ranges from 1%to 10%.Additionally,the applicability of the incipient motion formula to open channel flow is discussed.The formula can be considered suitable for calculating sediment starting velocity in open channel flow when the roughness of the ice cover is 0.The relative error validated by measured data is between 0%and 0.86%,meeting the precision requirement.