管内过冷流动沸腾CFD模型参数敏感性研究

采用CFD方法对燃料组件进行过冷流动沸腾数值模拟研究是反应堆热工水力分析的一项重要内容。本研究使用STAR CCM+基于欧拉双流体模型结合壁面沸腾模型对管内过冷流动沸腾进行数值模拟，得到了壁面温度、主流温度及空泡份额的分布。基于实验结果对网格模型、湍流模型、壁面沸腾模型及相间作用力模型的参数设置进行了敏感性分析。研究结果表明，对于欧拉双流体模型，并非网格量越多结果越准确，加热面第1层网格的高度对结果影响显著。湍流模型和曳力模型对计算结果影响较小，非曳力中的湍流耗散力及升力对结果影响较大。Li Quan或Hibiki Ishii汽化核心密度模型与Kocamustafaogullari气泡脱离直径模型组合对壁面温度及空泡份额的计算较准确。本研究可为反应堆燃料组件内过冷流动沸腾数值模拟提供参考依据。

Parameter Sensitivity of CFD Model of Subcooled Flow Boiling in Tube

The critical heat flux is essential to the operational safety of nuclear power plants, and it plays a vital role in the thermal-hydraulic and structural design of a fuel assembly. To improve the heat transfer efficiency of the reactor fuel assembly, it is necessary to accurately calculate the two phase flow boiling characteristics and the critical heat flux in the fuel assembly. Accurate simulation of subcooled flow boiling in simple geometry (such as round tubes, annular tubes, and rectangular channels) can lay a foundation for the research of boiling crisis phenomenon in complex structures (such as fuel rod bundle). Compared with single phase flow, mass, momentum, and energy transfer process occur at the interface of two phase flow. In addition to the conventional turbulence model and grid model, the interactions between liquid and vapor phases need to be characterized by various interphase forces. Furthermore, the wall boiling model is needed to describe the distribution of heat flux at the heating surface, which includes several empirical auxiliary models. Accurate simulation of flow boiling phenomenon requires the further study of many sub-models in numerical calculations. In this study, the commercial computational fluid dynamics package STAR CCM+ based on the Eulerian two fluid model combined the wall boiling model was used to simulate the subcooled flow boiling in a vertical tube, and obtain the distribution of wall temperature, mainstream temperature and void fraction. Based on the experimental results, the sensitivity analysis of the parameter settings of the grid models, turbulence models, boiling models and interphase force models was carried out. The results demonstrate that for Eulerian two fluid model, with the increase of the number of grids, the results are not more accurate. The height of the first layer of grid on the heating surface has a significant effect on the calculations. By setting different first layer grid heights for comparison, it is found that when the grid height is low enough to make the minimum y+<40, the local parameters in flow boiling calculation would change dramatically (especially the void fraction near the wall), which would affect the stability of numerical calculation. The calculation results under different turbulence models and drag force models have relatively small differences while the turbulent dissipation force and lift force in the non drag force have a greater impact on the results. The combination of Li Quan or Hibiki Ishii nucleation site density model and Kocamustafaogullari bubble departure diameter model can accurately calculate the wall temperature and void fraction. This study can provide more references for the numerical simulation of subcooled flow boiling in the fuel assembly.