黏性细颗粒泥沙絮凝发育时空过程的数值模拟  

Temporal and spatial variations of the flocculation process of fine cohesive sediments:a numerical simulation

作　　者：杨铁笙[1] 赵明 

机构地区：[1]清华大学水沙科学与水利水电工程国家重点实验室,北京100084 [2]广西长江天成投资集团有限公司,广西南宁530000

出　　处：《水利学报》2015年第11期1312-1320,共9页Journal of Hydraulic Engineering

基　　金：国家自然科学基金项目(51179087)

摘　　要：以Smoluchowski方程为基础,用数值模拟方法研究黏性细颗粒泥沙絮凝-沉降的时空过程。模拟设定泥沙最小基本颗粒粒径5μm,絮团分形维数1.78,模拟高度1.75 m,模拟总时长300 min,初始条件为各级泥沙颗粒-絮团浓度各向均匀分布,入口、出口无泥沙通量。模拟给出泥沙质量浓度、絮团平均粒径、絮团粒径分布等参数的时空变化过程。模拟发现:各个高度上泥沙质量浓度随时间变化的曲线均呈平缓衰减、快速下降与趋零三个阶段,其形状相似;位置越低,曲线的显现时间越滞后。絮团质量加权平均粒径随时间变化过程存在升涨-高峰-衰落三个阶段。碰撞效率系数越大,峰值越高;位置越低,峰现时间越滞后。本文还以泥沙质量浓度随时间变化为例,比较了数值模拟与絮凝试验的测量结果,二者基本一致。This paper presents a numerical study on the flocculation and sedimentation process of fine cohe-sive sediment particles based on the Smoluchowski equation and its extended model. The simulated mini-mum size of sediment particles is 5.0μm,the floc fractal dimension is 1.78,and the height and diameterof the simulated sedimentation measuring cylinder are 1.75 m and 0.14 m,respectively. The simulated sedi-mentation time is 300 min. Initial conditions for this simulation include a uniform distribution of sedimentparticles and flocs in all directions,and zero sediment flux at the inlet and outlet of the simulated space.Temporal and spatial variations of some key parameters were simulated,including sediment concentration,average size of flocs,and size distribution of flocs. The impact of collision efficiency coefficient on simulat-ed flocculation processes was also investigated. Simulation results show that sediment concentration at anyheight all decreased monotonically, and the concentration- time curve has three stages, namely, gentleglide,steep drop,and diminishing to zero. For flocs the competition between aggregation growth and sedi-mentation resulted in an average floc size variation curve which is very similar to an＂error function＂,withits peak indicating the balance point of the two competitive processes. Simulated sediment concentrations atthe depth of 1.0m agrees well with measured data. This study also discussed future prospects regarding theapplication of the Smoluchowski equation on sediment flocculation processes, and revealed some aspectswhich require further investigation.

关 键 词：絮凝 SMOLUCHOWSKI方程 数值模拟 时空变化 分形 

分 类 号：TV141[水利工程—水力学及河流动力学]