水流紊动对长江口细颗粒泥沙沉降速度影响机理性试验研究

For fine sediments, settling velocity is a sensitive and fundamental parameter for determining the suspended sediment dynamics and near-bed sediment flux (deposition and erosion) in riverine, estuarine and coastal surroundings. During the past, many efforts have been done to improve our understandings on the settling characteristics. But, very limit attention is paid on the effect of turbulence on the settling velocity. Based on laboratory experiment, this study aims to investigate the relationship and correlation between settling characteristics and turbulence. The mechanism of the impact of turbulence on the vertical suspended sediment concentration profile will be analyzed, and it will be illustrated by an empirical formula. Finally, the experimental result and the formula will be verified and examined by 3D numerical modeling in the site of the Yangtze Estuary. This research tries to improve our knowledge on fine sediment dynamics and help us to determine the settling velocity in numerical and physical modeling works.

泥沙沉速是泥沙研究基础理论体系中最核心的物理量之一，它是直接表征泥沙动力学特征和影响悬沙输运、河床底部边界冲刷、淤积通量重要的控制参数。国内外对细颗粒泥沙沉速问题及沉降过程基本特性等相关问题虽然进行了不少探索，但在水流紊动对细颗粒泥沙沉速影响的问题上研究还很不够。为定量研究水流紊动对河口细颗粒泥沙沉降速度的影响，本研究拟以长江口北槽现场原状悬沙和海水样为研究对象，在前期自主设计开发的大型可温控自动搅拌沉降试验筒基础上，加入栅格自动造紊设备，通过不同典型含沙量条件下的系列试验，改进已有的静水沉速经验公式，给出不同条件下水流紊动与细颗粒泥沙沉速的相关关系。此外，本研究还利用三维数学模型来评估建立的经验公式对长江口最大浑浊带悬沙浓度剖面变异特性模拟的改进效果。

泥沙沉速是泥沙研究基础理论体系中一个基本而又核心的物理量，它是直接表征泥沙动力学特征和影响悬沙输运、河床底部边界冲刷、淤积通量最重要的控制参数之一。国内外对细颗粒泥沙沉速问题及沉降过程基本特性等相关问题虽然进行了不少探索，但在水流紊动对细颗粒泥沙沉速影响的问题上研究还很不够。本研究拟以长江口现场原状悬沙和海水样为研究对象，改进已有的沉降筒试验设备；通过系列试验，研究水流紊动强度对长江口细颗粒泥沙沉降过程和沉速的影响；建立了细颗粒泥沙沉速经验公式，并利用数学模型验证了试验结果对细颗粒泥沙垂向剖面结构的修正效果。