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床面泥沙颗粒由于其相对暴露度及外形的不同,即使在同样水流条件下,颗粒附近的水流结构也不相同,进而影响到颗粒的受力不同,主要表现在颗粒拖曳力系数和上举力系数的不同。在白玉川提出的双向相对暴露度概念及拖曳力系数、上举力系数与纵向相对暴露度之间关系的基础上,分析发现,拖曳力系数介于1.00~1.22区间的概率大于92%,平均值为1.11;拖曳力系数与上举力系数比值平均值随沙粒雷诺数变化而变化,但在颗粒雷诺数大于25 000时,拖曳力系数与上举力系数比值平均值趋于常数1.28。将拖曳力系数和上举力系数引用到泥沙起动底流速公式中,得到了散粒体泥沙起动流速公式。实测资料验证表明,起动流速公式与实则资料吻合良好,间接地验证了提出的推移力系数值及上举力系数值是正确的。
Bed sediment particles due to their relative exposure and the appearance of different, even in the same water flow conditions, the water near the particle structure is not the same, thus affecting the force of different particles, mainly in the particle drag coefficient and lifting The difference of force coefficient. On the basis of the concept of two-way relative degree of exposure proposed by Bai Yuchuan and the relationship between towing force coefficient, lifting force coefficient and longitudinal relative exposure, it is found that the probability of drag coefficient is between 92% and 1.00% The value of drag force coefficient to the uplift force coefficient varies with the Reynolds number of sand particles. However, when the Reynolds number of particles is greater than 25 000, the average value of the drag force coefficient and the uplift force coefficient tends to 1.28. The drag force coefficient and uplift coefficient are introduced into the formula of sediment bottom flow rate, and the formula of sediment flow velocity is obtained. The test results show that the formula of starting flow rate is in good agreement with the real data, which indirectly proves that the values of pushing force coefficient and lifting force coefficient are correct.