棒束通道内定位格架搅混特性PIV可视化研究

定位格架作为燃料组件中重要的组成部件之一，不仅在结构上固定燃料棒，而且在燃料组件内热工水力性能同样显著，特别是对工质的搅混性能直接关系到反应堆的经济性和安全性，因此有必要对燃料组件内定位格架搅混特性进行研究。本文通过粒子图像测速（PIV）技术开展了棒束通道内定位格架上下游流场的可视化研究，对比了有无格架棒束通道内流场的分布特征，定量分析了定位格架对棒束通道流场搅混的贡献。对不同流速下定位格架下游横纵速度的沿程变化特性进行研究，发现了不同流速作用下定位格架对横向、轴向速度的促进和抑制规律。另外，通过速度均方根对下游的湍流特性进行了评估。实验结果可为数值计算提供全场的数据验证，并可为定位格架设计和优化提供基础。

Visualization Experiment of Mixing Characteristic of Spacer Grid in Rod Bundle Using PIV Technique

Spacer grid is one of important components in fuel assembly. Not only do spacer grids provide rods with supporting and positioning, but also their thermal hydraulic performance is significant in fuel assembly. The cross-mixing of spacer grid for the working fluid is closely related to the economy and safety of reactor. Therefore, an investigation on mixing characteristic of spacer grids in fuel assembly is indispensable. A visualization research on flow field upstream and downstream the spacer grid was implemented by the particle image velocimetry (PIV) technique. In order to obtain a global understanding of mixing characteristic of spacer grids, comparisons of the velocity distribution in a rod bundle with and without spacer grids were performed, and the mixing contribution of spacer grids for flow field was quantitatively evaluated. The lateral velocity and axial velocity downstream the spacer grid for the different inlet boundary conditions were obtained, and mixing characteristics of spacer grids for lateral velocity and axial velocity were analyzed under different flows. In addition, the turbulence characteristics downstream the spacer grid were assessed. Experimental results benefit the development and evaluation of spacer grid, and also provide the whole-field validation for numerical simulations.