床面附近泥沙运动的分析

Analysis of near-bed sediment motion

基于水、沙两相的分相测量试验结果,分析了床面附近泥沙颗粒的脉动和力学特性,指出床面附近的泥沙运动有着特殊的力学机制:颗粒相具有较强的非湍流脉动,其产生的脉动应力对颗粒的运动起着重要作用。论述了沙粒在水流中从推移运动到扬起悬浮的物理过程,讨论了过去一些理论中存在的问题和不足,概括了泥沙颗粒在水流中从床面扬起的基本模式,运用两相流理论分析了沙粒在水流中扬起的动力学机理。根据颗粒运动的垂向动量平衡原理,对泥沙颗粒的垂向浓度分布规律作了新的分析解释。证实了除浓度梯度之外,颗粒相的垂向脉动强度梯度也是泥沙扩散的重要扩散势,进一步揭示了悬移质浓度垂线分布存在两种类型的内在机理。

Based on the experimental data obtained by using two-phase measuring technique, the fluctuating features and mechanism of sediment movement near the bed in water-sediment flow were analyzed. The special mechanism of sediment movement in the near-bed layer is found in that sediment particles have very intense non-turbulent fluctuation near the bed, resulting in fluctuating stress, which will greatly influence sediment movement. From this point of view, a systematical knowledge on the physical process of sediment particles being raised in water flow is presented. Some problems and insufficiencies existing in traditional theories are discussed, from which a new basic model of sediment entrainment is suggested. Using the two-phase flow theory, the mechanism of sediment entrainment are analyzed in detail. Finally, the profile of sediment concentration are investigated by the theory of momentum equilibrium of particle movements in vertical direction. It is demonstrated that, besides the gradient of sediment concentration, the gradient of fluctuating velocity intensity of particles is also a significant diffuse force, which further gives a reasonable explanation for the mechanism of two types of profiles of sediment concentration.