河口分层流扩散与混合对流动演化的耦合响应

Stratified density flow is popular in estuaries where fresh runoff of rivers and marine saline water come across. The buoyancy effects and vertical mixing due to density differences are involved in not only mass transport but also internal momentum exchange and energy transfer as well as evolution of turbulence. The stratification resulted from mixing responses to hydrodynamic by coupling functions, which significantly affects the internal characteristics of flow as well as estuarine water quality, sedimentation and even ecosystem development so that it is essentially one of focus in study of contemporary environment of estuaries. Based on that, our project will employ experimental and field observations, theoretical analysis and numerical computations to give deep research to the interaction between internal multi-scale hydrodynamic and diffusive mixing in stratified estuaries. The mechanism of coupling effects to each other will be explored for stratification, mixing and flow evolution in order to uncover the general and substantial disciplines of estuarine saline mixing and then establish parameterized equations for coupled mechanical relationship between the estuarine mixing and the flow evolution. The study outputs are expected to widen and deepen the scientific understanding of internal hydrodynamic process of estuaries and to be used for theoretical basis and guidance to analysis and numerical simulation of estuarine environment, which implies broad prospects for application in future practice.

在自然界的河口中，径流淡水和海洋盐水相遇交汇，密度分层现象十分普遍。由于密度变化而带来的浮力影响和垂向混合不仅关系到物质输运，还关系到水体内部动量和能量的交换以及紊动的变化，使得混合和分层与水动力交织在复杂的耦合关系中，成为影响水流内部流动以及水质、沉积乃至生态系统发展的重要因素，是河口环境研究中最为关注的内容之一。因此，本课题拟通过水槽实验、野外观测、理论分析和数值计算相结合的方法，研究河口分层流内部多尺度动力结构与扩散混合的相互作用和影响过程，探索河口条件下分层和混合与内部流动演化耦合作用的力学机制，揭示河口盐水混合的内在普遍规律，并建立描述河口混合与流动演化之间耦合动力作用和相互力学关系的参数化方程，研究成果将拓展和深化河口内部水动力过程的科学认识，具有较高学术价值，可为河口环境分析和模拟计算提供科学理论依据和指导，未来具有广阔的应用前景。

自然河口普遍存在的盐淡水密度分层现象是影响水流内部流动以及水质、沉积乃至生态系统发展的重要因素，是河口环境研究中最为关注的内容之一。本项目从环境力学角度，着重河口水体密度变化带来的浮力影响和垂向混合，结合混合和分层的时空状态，探索这一复杂耦合关系过程中物质输运、水体内部动量和能量的交换以及紊动掺混的变化。课题通过水槽机理实验、野外现场观测、理论分析和数值模拟等相结合的方法，研究了河口密度分层流多时空尺度动力结构与扩散混合的相互作用和影响过程，分析了径流、潮汐共同作用主导河口盐水状态和运动的基本物理过程，明确了对一定几何尺度的河口水流环境，两者的相对大小决定半月周期非平衡态盐水围绕准平衡态上溯的内在普遍性规律，阐明河口条件下盐水运动对外部驱动力及内部流动演化的力学响应机制在于密度分层、紊动混合和平流输运等主要过程之间的时空耦合变化，具有显著的空间分布性、时效性和非线性特征，其对外部作用的响应随驱动力之间对比程度不同而不同。研究成果拓展和深化了对河口复杂水动力过程的科学认识，具有较高学术价值，可为河口环境分析和模拟计算提供科学理论依据和参考指导，为未来应用研究奠定分析基础。