水流作用下水-浮泥界面失稳及物质交换机理研究

Fluid mud is related to large amounts of engineering and environmental issues. The destabilization and entrainment processes are important hydrodynamics of fluid mud under the effects of currents. The entrainment rate is an important parameter for the research on fluid mud transport. Most previous studies calculating the entrainment rate are based on the average flow velocity or critical shear stress, the results of which with large uncertainties. However, the process based study on the entrainment of fluid mud is rare. Therefore, study on the mechanism of destabilization and material exchange on the water-fluid mud interface is significant in both academic research and engineering practice. This study will be conducted by using lab experiments, numerical modelling and dimensional analysis. The evolution of overturning billows will be investigated by conducting quantitative measurement, and the destabilization types of fluid mud interface will be summarized. The two-phase model will be built and validated to better represent the destabilization and entrainment processes of fluid mud. The two-phase model will be further used to expand the parameter study scope of lab experiments. The entrainment rate can be obtained by combining the results of lab experiments and numerical modelling. Then the mechanism of destabilization and entrainment of fluid mud layer can be revealed. The study of this program will enrich the sediment dynamics and provide parameters and theoretical support for numerical models concerning the transport of fluid mud.

浮泥涉及大量工程、环境问题，在水流作用下浮泥交界面失稳及悬扬是浮泥重要的动力特性，浮泥悬扬速率是研究浮泥输运过程的重要参数。目前的研究主要基于水流平均特性或者浮泥自身特性计算浮泥悬扬速率，结果具有较大的不确定性，缺乏基于浮泥界面失稳过程推求浮泥悬扬速率的研究。本项目拟采用物理实验-数值模拟-量纲分析相结合的方法，对水流作用下水-浮泥界面失稳以及物质交换展开研究。通过对水-浮泥界面失稳时界面上漩滚物理尺度的定量化测量、分析，研究其成长变化规律，并总结浮泥界面失稳的主要类型；构建并验证适用于模拟浮泥界面失稳、悬扬的两相流数值模型，拓展物理实验参数；综合物理实验以及数值模型结果推求浮泥悬扬速率，从而揭示水流作用下水-浮泥界面失稳及悬扬机制。本项目成果可以丰富泥沙动力学学科内涵，为模拟浮泥输运过程的工程数学模型提供重要的参数和理论支撑。

浮泥是贴近于海床的高含沙水体层，具有很强的流动性，它在淤泥质河口海岸地区广泛存在，对河口海岸演变及航道工程安全具有直接影响。浮泥运动特征是河口海岸学研究领域的重点和难点，而水流作用下浮泥失稳及悬扬过程是浮泥运动研究的重要内容，浮泥悬扬速率是研究浮泥输运过程乃至河口海岸地貌演变相关研究的重要参数。目前的研究主要基于水流平均特性或者浮泥自身特性计算浮泥悬扬速率，结果具有较大的不确定性。而基于浮泥界面失稳过程推求浮泥悬扬速率的研究较为缺乏。本项目对水流作用下水-浮泥界面旋滚结构以及物质交换机理展开研究。通过对水-浮泥界面失稳时界面上漩滚物理尺度的定量化测量、分析，研究其成长变化规律，并总结浮泥界面失稳的主要类型；综合物理实验以及数值模型结果推求浮泥悬扬速率，揭示了水流作用下水-浮泥界面失稳及悬扬机制。采用体积Richardson数量化悬扬过程中分层流体系密度层化效应与紊动动能的相对大小，拟合得到其与无量纲悬扬速率E的经验关系表达式。本项目成果可以丰富河口海岸学学科内涵，为模拟浮泥输运过程数学模型提供重要的参数和理论支撑。

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