挟沙水流卡门常数的理论研究

挟沙水流的流速分布,特别是其中的卡门常数,一直是冲积河流水力学研究的热点问题之一.实测资料表明挟沙水流流速分布仍遵循对数流速分布规律,但在主流区的卡门常数要小于清水时的卡门常数,而在近底区的卡门常数与清水基本一致.在引入颗粒切应力的基础上,从理论上推导了同时适用于主流区和近底区的统一流速分布模型.利用该流速分布模型,得到挟沙水流的卡门常数沿垂线是变化的结论,即从近底区的约0.4渐变到主流区的小于0.4.并给出了主流区卡门常数的理论表达式,认为主流区卡门常数与近底区的泥沙浓度和泥沙粒径有关.该卡门常数的理论公式与实测资料较为吻合.

Theoretical Study on Kaman Constant in Sediment-Laden Flow

Velocity distribution in sediment-laden flow, especially its Karman constant, is one of the most important issues in fluvial hydraulics. The measured data show that the velocity distribution in sediment-laden flow still obeys the logarithmic distribution law, but the Karman constant is smaller than that of clear water in main flow region, and almost is same as that of dear water in near bed region. Based on the introduction of sediment grain shear stress, a unified velocity distribution model, region, was derived from theoretical analysis. By use of which is suitable for both main flow region and near bed this model, it is demonstrated that the Karman constant is varied in vertical distance from near 0.4 in near bed region to below 0.4 in main flow region. Also a theoretical expression for Karman constant in main flow region is given, which considers the Karman constant in main flow region to be associated with sediment concentration and sediment diameter in near bed region. The results from this equation of Karman constant agree with measured data.