电解质及水流剪切对高浓度粘性沙悬浮液流变参数的影响

The investigation on the influences of electrolyte and flow shear on rheological properties of highly-concentrated cohesive sediment suspension is a important subject in the context of sediment transport dynamics, and it is of fundamental importance for clarifying the mechanisms of hyper-concentrated flow transport, debris flow and estuarine sediment movement. By means of experiment measurement and theoretical analysis, this project studies the influence of electrolyte (valence of cation and concentration) on the rigidity (or viscosity) and yield stress of highly-concentrated cohesive sediment suspension under a static condition, then discusses a possible physical mechanism involved in the role which is played by electrolyte in determinations of rigidity and yield stress of the suspension, and finally derives two mathematical expressions to calculate rigidity and yield stress of the suspension by incorporating influences of all factors such as electrolyte condition, primary sediment concentration, median size and size distribution of sediment particle. Flow shear on the one hand can improve the collision frequency of sediment particle, subsequently accelerating the flocculation development of cohesive sediment; on the other hand, it can also increase the possibility of floc breakup, therefore inhibiting the flocculation process. This project also investigates the variation of yield stress of high-concentrated cohesive sediment suspension as the suspension undergoes the transition from the laminar state to the turbulent state, and, more importantly, attempts to discuss the physical mechanism involved in the influence of flow shear on yield stress of the suspension using methods of image processing and sampling observation.

揭示电解质和水流剪切对高浓度粘性沙悬浮液流变参数的影响，是泥沙运动力学的一个重要课题，是认识高含沙水流输运、泥石流运动以及河口泥沙运动等方面机理的基础。本申请拟通过实验和理论分析，研究静水条件下，电解质阳离子化合价和电解质浓度对高浓度粘性沙悬浮液刚度系数和屈服应力的影响，探讨电解质条件对悬液刚度系数和屈服应力作用的物理机理，推导能涵盖电解质、初始泥沙浓度、泥沙颗粒中值粒径及粒径级配因素影响的刚度系数和屈服应力计算表达式；水流剪切一方面能提高颗粒碰撞频率，促进絮凝发育；另一方面也能增大絮团破裂的可能性，抑制絮凝发育。课题将研究水流从层流流态逐渐转化为紊流流态时高浓度粘性沙悬液屈服应力的变化规律，借助于图像处理和取样观察手段，探讨水流剪切对高浓度粘性沙悬液屈服应力作用的物理机制。

黏性细颗粒泥沙絮凝研究是泥沙运动力学的一个重要课题，是认识高含沙水流输运、泥石流运动以及河口海岸冲淤演变等规律的基础。本项目围绕着黏性沙絮凝这一课题，开展了以下五个方面的基础性研究：（1）开展了不同泥沙体积浓度对水沙悬液粘度系数影响的实验研究，发现随着泥沙浓度从低到高的逐步增加，粘度系数呈现先缓慢增加，然后快速增加，最后再次缓慢增加这一特殊现象，并推导了数学表达式；（2）开展了紊动水流中黏性沙絮团结构实时变化的实验研究，发现絮团的二维分形维数（基于周长的分形维数）先减小（增加），最后达到平衡状态。水流强度越大，平衡状态越早达到。（3）采用信息熵理论模拟了水流剪切中黏性沙絮团粒径的实时变化特征，构建的模型具有较高的拟合精度；（4）开展了低浓度和高浓度黏性沙悬液絮凝-沉降的观测实验，发现无论低浓度还是高浓度，泥沙悬液浓度（或液面）呈现先快速下降，然后缓慢下降，最终达到稳定状态，提高加入的电解质的浓度和阳离子化合价能产生显著影响；初始沉降高度、泥沙浓度和泥沙粒径对沉降过程均有明显影响。（5）推导了黏性沙絮团的静水沉速公式，该公式考虑了基本泥沙颗粒粒径的非均匀性；采用信息熵理论推导了泥沙在水沙悬液中的阻止沉速公式，具有较高的精度。本项目的研究成果属于基础性研究成果，丰富了人们对泥沙运动力学特别是黏性沙传输过程的理解和认识，特别是推导的紊动水流中絮团粒径变化模型、絮团静水沉速公式和泥沙阻止沉速公式，能够为泥沙工程界采用，模拟河流、湖泊、水库、河口和海岸等水域中黏性泥沙的输移过程。