棒束内湍流流动特性的PIV与CFD研究

在压水堆燃料组件的定位格架下游，局部扰动沿流动方向逐渐衰减，流场最终趋于稳定。光滑棒束区冷却剂的湍流流动和交混特性是影响反应堆经济性和安全性的重要因素，有必要进行深入研究。本文采用粒子图像测速（PIV）与数值模拟(CFD)相结合的方法，对3×3小规模棒束内水的流动特性进行研究，得到了一阶平均流速以及二阶湍流统计信息。结果表明，中心子通道的速度明显高于棒间隙区，但轴向均方根速度呈现出相反的变化趋势。在相邻子通道横向速度梯度的作用下，棒束内出现了大尺度的流量脉动现象，且脉动波长随雷诺数的增加而增大。此外，实验得到的湍流交混系数较压水堆采用的Castellana公式预测值偏高10%左右，这一偏差随雷诺数的增加有减小的趋势。

PIV and CFD Study of Turbulent Flow Behavior in Rod Bundle

At the downstream of the spacer grid in a PWR fuel assembly, local disturbance damps out along the flow direction and the flow returns to stable eventually. The turbulent flow and mixing behavior of the coolant are key factors affecting the economy and safety of a nuclear reactor, and need in-depth investigations. In the present paper, the turbulent flow of water in a 3×3 rod bundle was studied using PIV (particle image velocimetry) and CFD. First-order mean velocity and second-order turbulent statistics were obtained. It is found that the velocity in the central subchannel is higher than that in the gap region, but the streamwise root-mean-square velocity behaves inversely. Large-scale flow pulsation induced by the strong streamwise velocity gradient between adjacent subchannels, is observed in the rod bundle, and the wave length increases with Reynolds numbers. In addition, the measured turbulent mixing coefficient is 10% higher than that predicted by the Castellana correlation for PWRs, but this deviation reduces with the increase of Reynolds numbers.