潮汐条件下温排水紊动扩散机理试验与数值模拟研究

The mechanism of turbulent diffusion for cooling water in tidal flow is essential to the research on thermal discharge from thermal and nuclear power plants. The simultaneous measurements for velocity and concentration fields are performed for the thermal discharge into the tidal flow from the bottom, by use of high resolution technology with high sampling frequency. With the combination of theoretical and experimental analysis, the regulations for the velocity, concentration, turbulent intensity, Reynolds stress, and turbulent diffusion flux are investigated for typical cross-section in detail. The turbulent structure due to the tidal force is revealed, and the turbulent viscosity and diffusivity are also obtained. Based on the experimental results, the three-dimensional mathematical model for cooling water is verified, and corresponding parameters are modified. The three-dimensional model is established under the combined action of tidal flow, the buoyancy effects due to the temperature difference, as well as the turbulent diffusion. The research results are beneficial for the understanding of hydraulic and thermal mechanisms for cooling water, the enrichment of theories in environmental hydraulics, and the extensive application of three-dimensional model in engineering. Also, the research results can provide key technology and theoretical guide for engineering design, environmental influence assessment, and overall planning and management performed by government. Therefore, the research results are significant in academic and applicative aspects

潮汐条件下温排水的紊动扩散机理是进行滨海火、核电厂温排水研究的核心问题。本项目拟采用高分辨率、高采样频率的PLIF-PIV测量技术，对温排水底部入射环境潮流的排放方式进行瞬时流场、瞬时浓度场的同步测量，结合实验与理论分析，系统研究排口近区特征断面流速、浓度、紊动强度、雷诺应力、紊动扩散通量等物理量的随潮变化规律；揭示潮动力作用下温排水的紊流结构；获得紊动粘性系数与紊动扩散系数，探寻紊动扩散机理。以水槽试验成果为基础，对温排水三维数学模型进行验证和紊流参数改进，构建综合反映潮流、温差浮力效应以及紊动扩散的三维模型。研究成果将加深对滨海温排水水力、热力机理的认识，丰富环境水力学的基本理论，推动温排水三维数学模型在工程中的应用，为工程设计、环境影响评价以及政府部门统筹规划与管理沿海热排放提供技术支撑与理论指导，具有重要学术意义及实用价值。

沿海经济高速发展带来的海洋环境污染问题日益突出。水温是重要的水质和生态环境要素。水温是重要的水质和生态环境要素。沿海密集分布的火、核电厂每年至少将上千亿吨的温排水排入海域，对海洋生态系统造成无法回避的热影响。温排水以浮射流的运动形式排入环境海域。潮流作为河口及海洋中水流最为普遍的运动形式，是温排水输运的主要载体。系统掌握潮流中浮射流的初始稀释特性，对于有效控制废热排放，减小温排水对海洋环境的热影响具有重要意义。. 潮流中浮射流的运动受初始动量、浮力、潮流共同影响，问题比较复杂。受模拟技术与测量技术发展水平的限制，一直缺乏系统深入的研究。本文采用实验与数学模型相结合的方式，深入研究了潮流环境下浮射流的演变过程、掺混稀释规律和紊动扩散特性。首次研发了大范围、高帧频PIV-PLIF同步测量系统，实现了流场与浓度场的大面积同步量测，为潮流环境下射流实验研究奠定了基础。在研究分析天然潮汐水域浮射流特征基础上，提出了潮型与浮射流的概化模型，建立了长周期、高精度潮汐模拟系统。在详细分析潮流紊动特性基础上，针对潮汐水域温排水的典型排放方式—垂直浮力射流，首次采用PIV-PLIF技术研究了完整潮周浮射流纵轴面的流场与浓度场，揭示了浮射流的湍流结构和随潮扩散规律，提出了纵轴面射流轴线与轴线稀释度计算公式。采用三维数值模拟方法深入研究了射流的空间涡流结构、浓度结构、分叉现象、射流轴线的随潮变化，提出了射流轴线和稀释度的计算公式。数学模型和实验两种研究手段互为补充，系统揭示了垂直紊动浮力射流的随潮演变规律和掺混稀释特性。研究成果不仅为潮汐水域废热水处置工程的设计与生态环境影响评估提供了科学支撑，而且对于推动海洋环境中污染物的输运规律研究、促进环境水力学中射流理论的发展具有重要意义。