脉动流条件下5×5环形燃料阻力与流量分配特性研究

Investigation on Characteristics of Resistance and Flow Distribution of 5×5 Annular Fuel Rod Bundle Channel under Pulsating Flow Condition

环形燃料棒束通道相较于传统实心棒束通道,具有增强冷却能力、提高功率密度等优点,其特殊几何形状使阻力特性与流量分配特性密切相关。在脉动流条件下,环形燃料内外流道流量呈周期性波动,影响冷却剂换热效率,威胁核反应堆安全。本文基于计算流体动力学(CFD)方法对5×5环形燃料棒束通道建立模型,在稳态与脉动流条件下开展模拟计算,模拟结果与粒子图像测速(PIV)实验测量速度场、摩擦阻力系数经验公式相比具有一致性。计算分析了内外流道摩擦阻力系数随雷诺数的变化规律,稳态条件下环形燃料的流量分配比(内流道流量比外流道流量)与压降比呈负相关;脉动流条件下,周期平均流量分配比与脉动频率呈负相关,与脉动振幅呈正相关。

Compared to the traditional solid rod bundle channel,the annular fuel bundle channel has the advantages of enhancing cooling capacity and improving power density,and its special geometry makes the resistance characteristics closely related to the flow distribution characteristics.Under the pulsating flow condition,the flow rate in the inner and outer channels of annular fuel fluctuates periodically,which affects the heat exchange efficiency of coolant and threatens the safety of nuclear reactor.In this paper,a model of 5×5 annular fuel rod bundle channel is established based on computational fluid dynamics(CFD)method,and simulation calculation is carried out under steady-state and pulsating flow conditions.The simulation is benchmarked with the experimental velocity field measured with PIV and the friction factors predicted by the empirical correlation,and the results show good agreement.The variation characteristics of the friction factors of the inner and outer channels versus the Reynolds number are analyzed.Under the steady-state condition,the flow distribution ratio(inner channel flow versus outer channel flow)of the annular fuel is inversely proportional to the pressure drop ratio.Under the pulsating flow condition,the periodically averaged flow distribution ratio is inversely proportional to the pulsating frequency and proportional to the pulsating amplitude.