方形组件紧密栅格内非稳态流动行为的研究

棒束子通道间冷却剂的交混作用能显著降低棒束周向壁面的温差，为进一步了解紧密栅棒束内特殊的流场结构，以水为工质，对P/D=1.1的双排六棒束方形通道内的流动进行了试验研究与数值模拟。采用流场示踪方法，在Re =2 000～40 000范围内拍摄了紧密栅内棒壁间瞬态流动可视化信息，捕捉到大尺度类周期性脉动结构，并获得了该脉动流的相关特征参数。结果表明：当Re≥5 000时，大尺度脉动流发生，并在实验工况内呈很强的周期性，脉动流的波长与Re无关，脉动主频率与Re成正比；采用SSG湍流模型对相同截面通道内的流动进行了非稳态计算，模拟出棒壁狭缝处的大尺度类周期性脉动行为，计算所得脉动流各项参数与试验值符合良好。

Investigation on Unsteady Flow Behavior in Tight Square Lattice

The mixing of cooling fluid between two adjacent sub-channels in rod bundles reduces significantly the wall temperature difference along the perimeter of the rods. In order to study the special structure of flow in tight lattice, experiment investigation and numerical simulation were performed in a 2×3 square channel with P/D=1.1. Dye tracers were adopted in the experiment to visualize the detailed flow structure in the narrow gap between rod and wall. The Re was varied from 2 000 to 40 000. Large scale quasi-periodic oscillation was observed. Some characteristic parameters of oscillation were obtained. The results show that the large scale oscillation occurs at Re ≥5 000. The wavelength of oscillation is independent of Re, whereas the oscillation frequency increases proportionally with Re. Large scale quasi-periodic oscillation in the same cross section is also obtained using CFD simulation with SSG turbulent model. The calculated characteristic parameters agree well with the measured data.