扩散对流分层结构的湍流动力特征研究

Diffusive convection (DC) widely occurs in nature and industry processes. It has been extensively studied by oceanographers due to its importance in ocean (e.g. the interaction of water masses, its role in the ice-melting and so on). In order to accurately qualify the contribution of DC to the ocean circulation and transport, it is necessary to know the turbulent and dynamic properties of DC multilayer structures. In this project, we would take the velocity, temperature and salinity measurements under different parameters (density ratio, buoyancy frequency and so on) by using the laboratory experiments and direct numerical simulations. Therefore, we can explore the turbulent and dynamic characteristics of multilayer structures, including large-scale circulations within the same mixed layer, the coupling between different mixed layers, and the dynamic structure within the interface. In addition, the outcome of the experiments and simulations will be tested and applied by using the ocean in situ observation or the collected history data. These findings would shed more light on the formation of multilayer structure and the heat/salinity transport process, which subsequently has broad impact on the DC flows occurring in nature, especially in ocean, and industry processes.

扩散对流现象在自然界和工业过程中广泛存在。此现象由于在海洋的重要性得到大量研究，例如不同水团之间的入侵和对极地海冰融化的影响等。深入认识扩散对流中分层结构的湍流动力特征，是准确量化扩散对流在海洋环流和输运过程中作用的基础。本项目拟结合室内严格可控的流体力学测量和并行直接数值模拟，在不同参数范围（密度比和浮力频率等），同步测量扩散对流中分层结构的速度、温度和盐度的变化，探索混合层内大尺度动力结构及其关联机制，界面层动力结构特征及其温盐度分布等。同时，实验和模拟所得结果通过海洋现场观测及历史数据进行验证和应用。本项目研究成果有助于理解扩散对流分层结构的形成机制和热盐输运过程。也对认识自然界（尤其是海洋）和工业中包含扩散对流的流动现象有重要意义。

通过本项目的资助，开展了一系列扩散对流温盐台阶热力学规律和演化过程研究。通过室内严格可控的流体力学测量，结合海洋模式以及海洋现场观测数据，提出了在大的密度比范围内普适的扩散对流垂向热通量参数化方案，该方案对于准确评估扩散对流对北冰洋的热、盐通量输运和海洋混合的影响非常重要。这些参数化方案应用于海洋模式，有助于得到更接近真实的海洋模拟和预测。另外，根据扩散对流中的界面-混合层结构特征，研究了海底混合层的结构和湍流特征，提出新的确定混合层厚度的方法：“集合法”。相比于现有方法，该方法可以更精确确定混合层厚度，这对于研究混合层内的动力，生态和物质变化至关重要。通过该方法评估全球海洋底混合层厚度空间分布变化从数米到近千米，平均约50米。对底混合层内湍流分析表明海底混合受地形，內波和底层流的影响。通过本项目的资助，发表SCI论文9篇，获批4项专利和培养了研究生3名。