颗粒惯性效应对悬移质不平衡输沙的影响机理研究

Non-equilibrium transport of suspended sediment is one of difficulties and emphases in the field of river dynamics and sediment movement because it is the foundational reason for the scouring and silting in alluvial rivers. However, the complex movement of non-equilibrium transport affected by a number of factors leads to that many unsolved problems still exist, and need further study. Especially, particle inertia has a significant effect on non-equilibrium transport of suspended sediment, but the mechanism of particle inertia effect is not so clear that current theories cannot precisely describe it. Therefore, in this study, based on the two-fluid equations for solid/liquid two-phase flows, by deriving the constitutive relation for the drift velocity of non-equilibrium transport of suspended sediment by employing the perturbation method, we aim to establish the non-equilibrium transport model equations considering the effect of particle inertia. Combining the theoretical model and corresponding experimental observations, the following topics will be the main concerns of this study: (1) investigating the spatial variations of sediment concentration distributions of non-equilibrium transport; (2) discussing the effect of particle inertia on the sediment diffusion in the vertical direction and the variations of concentration distributions along a river; (3) analyzing the effects of particle turbulence and interaction among particles on the saturation recovery coefficient under different particle inertia conditions. As a fundamental element of research on sediment-laden flows, the studies of this proposal are expected to provide the foundation for a better understanding of the non-equilibrium transport of suspended sediment.

悬移质不平衡输沙是引起冲积河流河床冲淤变化的根本原因，是泥沙运动力学和河床演变学的核心。但由于受到多种因素的影响，涉及的物理过程较为复杂，迄今仍有诸多问题尚待深入研究。其中，颗粒惯性效应对不平衡输沙运动特性存在重要的影响，但目前其作用机理并不明确，现有理论尚未给出准确的力学数学描述。本项目拟基于固液两相流理论，引入弥散速度的概念，利用摄动法推导不平衡输沙条件下固相颗粒弥散速度的本构关系，建立能够反映颗粒惯性效应影响的悬移质不平衡输沙基本方程。以此为基础，结合实验研究，分析不平衡输沙条件下泥沙浓度的空间分布变化规律，探讨颗粒惯性效应对垂向泥沙扩散和沿程浓度变化的影响机制，研究颗粒紊动、颗粒间相互作用等颗粒惯性效应对恢复饱和系数的影响，从而揭示颗粒惯性效应对悬移质不平衡输沙的影响机理。通过本项目的研究，可深入认识悬移质不平衡输沙运动规律，促进不平衡输沙理论研究的发展。

悬移质不平衡输沙是引起冲积河流河床冲淤变化的根本原因，影响因素众多，物理过程复杂，迄今仍有诸多问题尚待深入研究。其中，颗粒惯性对悬移质不平衡输沙的影响尚未形成明确的认识，理论上也未给出准确的力学数学描述。针对此问题，本项目开展了系统研究，取得的重要成果如下：.(1)基于固液两相流的理论，引入弥散速度的概念，利用摄动法推导了不平衡输沙条件下固相颗粒弥散速度的本构关系，建立了能够反映颗粒惯性效应影响的悬移质不平衡输沙基本方程；.(2)以此为基础，推导了低浓度条件下的浓度分布方程，并与已有公式进行了对比分析，阐明了不同公式的应用条件；.(3)结合实测数据，分析了不同条件下泥沙浓度的空间分布变化规律，结果表明本文理论无论泥沙浓度和颗粒粒径如何变化，计算值均能与实测值相吻合，验证了理论的正确性；.(4)阐明了颗粒惯性对不平衡输沙的影响，随着颗粒惯性的增大，沿程悬移质泥沙在垂向上的扩散速度逐渐变慢；.(5)揭示了颗粒紊动、颗粒间相互作用等颗粒惯性效应对悬移质输沙的影响机理。结果表明，随着颗粒惯性的增大，浑水紊动作用对泥沙扩散系数的贡献逐渐减，颗粒自身紊动引起的泥沙扩散作用相对增强，颗粒碰撞作用对泥沙扩散的贡献也有所增加，但相对于颗粒自身紊动作用的变化，增加的幅度相对较小。