压水堆燃料组件长期处于高温、高压、高雷诺数湍流的运行环境中，燃料棒束通道内部的流型和传热方式，是堆芯热工水力设计的基础和决定反应堆安全裕量的重要因素。在燃料组件设计和研发的过程中，针对热工性能的传统研究方法包括试验研究方法和子通道分析方法，模型空间分辨率低，大量依赖试验关联式、半经验关系式、大安全裕量的保守性假设，难以捕捉棒束通道内局部精细流动信息，在深入认识燃料棒束内热工水力状态及规律，以及针对局部结构（如搅混翼、弹簧、刚凸等）的优化设计改进等方面具有一定的局限性。随着计算机硬件的长足发展，计算流体力学（Computational Fluid Dynamics，CFD）分析方法得到越来越广泛的应用，已成为探索和理解压水堆堆芯内复杂流动传热现象的重要分析手段。然而，CFD计算结果与燃料棒束试验数据之间往往存在较大的偏差，其原因主要来源于大部分流体计算程序未经过高精度的燃料棒束流动和传热试验数据验证，目前暂无统一的针对燃料棒束单相流动和传热的CFD最优化计算方法，关键计算模型及参数均根据计算者的经验进行设置。由于燃料棒束流动传热现象较为复杂，网格类型和尺寸、边界条件、湍流模型等的不恰当选择均将导致计算结果产生较大的偏差，以至于CFD方法在工业界的广泛应用遇到一定的困难。本文的研究目标是建立较为可靠的、经试验数据验证的三维单相CFD计算分析方法，并将其应用于带格架燃料棒束内三维单相流动和传热的模拟分析中，为后续CFD方法在燃料组件设计研发中的实际应用提供指导方向。论文主要包含三部分研究内容，首先针对国内外相关研究展开了广泛调研，包括关键模型和参数的影响、单相流动规律及评价指标、传热规律及评价指标等，在充分调研的基础上，建立了CFD计算分析流程，确定了关键计算模型和参数。其次，将该CFD方法应用于典型2×2燃料棒束内单相流动和传热的计算分析中，进一步考察了在含格架燃料棒束中网格基本尺寸对计算结果的影响，确定了兼顾计算效率和计算精度的最佳网格尺寸。通过对比分析，研究了格架关键结构（搅混翼、弹簧、刚凸）对关键流动传热参数（压降、横向流动、温度等）的影响，为后续格架的结构设计改进指明了方向。最后，针对全长多跨5×5燃料棒束内的典型流动传热特性开展了CFD数值模拟分析，并与试验数据进行了对比。计算所得各子通道内平均温度与试验测量值趋势相同，数据吻合良好，说明了本文所建立CFD数值模拟方法的合理性和准确性。
The Pressurized Water Reactor (PWR) fuel assembly is working in the high temperature, high pressure, and high Reynolds number turbulence flow condition. The flow pattern and heat transfer mechanism inside the fuel bundle channel are the basis of the thermal hydraulic design and a crucial factor to determining the reactor safety margin. In the process of fuel assembly design, traditional thermal-hydraulic evaluation methods are the system codes, or the sub-channel analysis codes, the resolution of these codes are quite coarse, and they rely on the experimental correlations, semi-empirical correlations, and many assumptions. Therefore, the traditional methods are unable to reflect the local three-dimensional flow and heat transfer characteristics and have certain limitations in understanding the thermal hydraulic performance in the fuel bundle, and the optimized design of local structures, such as mixing vanes, springs and dimples.With the dramatic development of computer technology, Computational Fluid Dynamics (CFD) methods have become more and more widely used, and have become an essential analytical method to explore and understand the complex flow heat transfer phenomenon in PWR fuel assembly. However, there is always a significant deviation between the CFD calculation results and the fuel bundle test data. The main reason is that most CFD methods have not been validated based on high-precision fuel bundle experimental data. The CFD models and critical parameters are always set according to the experience of the individual modeler. Due to the complex flow and heat transfer phenomenon in fuel bundles, improper selection of grid type and size, boundary conditions, turbulence models, will lead to significant deviations of the calculation results. As a result, the CFD methods have certain difficulties in the application in the industry.The paper aims to establish a reliable and validated three-dimensional single-phase CFD method, and apply it to the simulation of single-phase flow and heat transfer in fuel rod bundle. The method will be helpful and guides the practical application of CFD method in the fuel assembly design and development process. The paper contains three parts. Firstly, extensive literature research is carried out, including the CFD models, critical parameters, flow, and heat transfer evaluation methods. Based on the literature research, basic CFD modeling process, calculation models and key parameters are established. Secondly, the CFD method is applied to the calculation and analysis of single-phase flow and heat transfer in a typical 2×2 fuel rod bundle. The influence of the basic mesh size on the calculation results is investigated, then the optimal grid size that takes into account both computational efficiency and computational accuracy is chosen. The influence of the key structure of the grid (mixed vane, spring, dimple) on the flow and heat transfer (pressure drop, lateral flow, temperature) is studied, which indicates the direction for the optimization design. Finally, the CFD numerical simulation analysis is carried out for studying the typical flow heat transfer characteristics in the full-length multi-span 5×5 fuel bundle. The calculated average temperature in each sub-channel agrees well with the experimental data, which shows the reliability and accuracy of the present CFD method. The CFD results indicate that the buoyancy force has a significant influence on the flow structure in the rod bundle. Due to the effects of the buoyancy force, the highest velocity in the sub-channel moves from center to the vicinity of the heating wall.
