暴雨径流条件下分层水源水库异重流形成机制及水质响应预测

Aiming at the common problem of turbid water induced by storm runoff in stratified source reservoirs during flood period, through pilot study and numerical modeling,the formation mechanism of density currents and response of water quality to density currents are systematically investigated under storm runoff condition in stratified source reservoirs, and two-dimensional two-phase models of water quality are developed to predict the water quality under density currents in stratified reservoirs. The main research contents include three parts.1）Studying the condition and mechanism of formatting density currents induced by differences of sediment concentration and water temperature between inflow and ambient waters, developing a theoretical model for the formation of density currents and analyzing main factors influencing the formation of density currents. 2) Investigating the evolution of density currents with flow visualization, measuring the depth, velocity and length of density currents under varying conditions, analyzing the characteristics of flow resistance and mixing during the evolution of density currents, calculating the profiles of sediment concentration and sediment flux and water temperature structure during the evolution of density currents, exploring the response mechanisms of water quality under density currents in stratified water environments.3)Studying the characteristics of rheology and settling of sediment, developing two-dimensional two-phase water quality models for sediment, water temperature and hydrodynamics in reservoirs, simulating the temporal and spatial distributions of sediment concentration and water temperature under density currents in stratified reservoirs, and determining the zones of turbid water in reservoirs. The research outcome will provide scientific theoretical foundation on and direct theoretical support to the determination of the optimal water intake during flood period and the calculation of the rate of sediment deposition in stratified reservoirs.

针对分层水源水库汛期暴雨径流引起的普遍浑水问题，通过中试和数值模拟，系统研究暴雨径流条件下分层水源水库异重流的形成机制以及水质对异重流的响应，建立异重流条件下二维分层水库水质模型,准确预测水库水质。主要包括：研究进水及背景水体含沙量及水温差别共存时异重流的形成条件与机理，建立异重流形成的理论模型，分析影响异重流形成的主要因素；可视化研究异重流演变过程，测定不同条件下异重流厚度、运行速度及长度，分析异重流演变过程中的阻力和混合特性，计算异重流演变过程中的泥沙浓度场、泥沙通量以及水温结构，探求水温分层环境中异重流条件下的水质响应机制；研究泥沙的流变和沉降特性，构建泥沙、水温及水动力共同耦合的二维两相流水库水质模型，预测不同异重流条件下水库泥沙浓度和水温的时空分布，确定水库浑水的存在区域。该研究将为确定分层水源水库汛期的最佳取水口位置和计算水库淤积速率提供科学的理论依据和直接的理论支持。

汛期暴雨径流会在分层水源水库内部引起浑水、泥沙淤积和内源污染，通过模型中试、水库现场测试和数值模拟，系统研究暴雨径流条件下分层水源水库异重流的形成机制以及水质对异重流的响应机制，建立并验证异重流条件下二维分层水库水质模型。主要包括：（1）建立并验证了分层水库水温结构的数值模拟方法，运用 Fluent 软件数值研究了不同短波辐射强度及短波辐射衰减系数条件下温跃层的形成过程与特性；（2）现场测试了石砭峪水库降雨期间异重流及其对水温结构变化，暴雨径流主要对水库水温结构产生暂时和局部的影响；（3）当入流速度和泥沙浓度较低时，异重流表现为表层流；反之，异重流表现为潜流；其他情况下，表现为间层流；当入流速度为0.005m/s时，泥沙浓度1.25 g~7.50g/L，间层流的中间位置距离水面0.15m~0.23m，间层流厚度0.12m~0.14m；异重流的头部运动速度随浓度增加而增加，随时间延长而减小；（4）在弱分层水体中，随入流泥沙粒径0.05mm的泥沙所占比例的增加，间层流的分离点深度和间层流的厚度逐渐增大，异重流挟沙量逐渐减弱，水库底部沉沙量与入流总沙量之比约从28%提高至38%；（5）在跃温层温度梯度约为41-48℃/m条件下，入流流量和泥沙浓度及粒径均影响适宜排沙口的位置，随入流流量和泥沙浓度的增大，适宜排沙口处水深范围和中心点水深增大，适宜排水口处泥沙浓度增加；（6）出水口位置会影响异重流排沙量，位于上层的排沙量远远大于出水口位于中层和下层的排沙量；（7）根据间层流内水跃方程，推导了非分层水库间层流含沙量的关系方程；采用量纲分析原理确定了模型参数组合，建立并验证了分层条件下间层流含沙量模型，预测误差为±15%内；（8）建立并验证了基于FLUENT的分层水库异重流运动及水质数值模型，准确预测了异重流流速、水温及泥沙浓度的时空分布。研究成果将为确定分层水源水库汛期取水口位置优化和水库淤积及内源污染控制提供科学的理论和技术依据。