Passive safety system is the core feature of advanced nuclear power plant (NPP). It is a research hotspot to fulfill the function of passive safety system by improving the NPP natural circulation capacity. Considering that the flow behaviors of stopped pump pose a significant effect on natural circulation, both experimental and computational fluid dynamics (CFD) methods were performed to investigate the flow behaviors of a NPP centrifugal pump under natural circulation condition with a low flow rate. Since the pump structure may lead to different flows depending on the flow direction, an experimental loop was set up to measure the pressure drop and loss coefficient of the stopped pump for different flow directions. The experimental results show that the pressure drop of reverse direction is significantly greater than that of forward direction in same Reynolds number. In addition, the loss coefficient changes slightly while the Reynolds number is greater than 8 × 10⁴; however, the coefficients show rapid increase with the decrease in Reynolds number under lower Reynolds number condition. According to the experimental data, an empirical correlation of the pump loss coefficient is obtained. A CFD analysis was also performed to simulate the experiment. The simulation provides a good accuracy with the experimental results. Furthermore, the internal flow field distributions are obtained. It is observed that the interface regions of main components in pump contribute to the most pressure losses. Significant differences are also observed in the flow field between forward and reverse condition. It is noted that the local flows vary with different Reynolds numbers. The study shows that the experimental and CFD methods are beneficial to enhance the understanding of pump internal flow behaviors.

中文翻译：

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自然循环条件下NPP泵流动特性的实验和CFD研究

被动安全系统是先进核电站（NPP）的核心特征。通过提高核电厂的自然循环能力来实现被动安全系统的功能是一个研究热点。考虑到停泵的流动特性对自然循环有很大的影响，在实验和计算流体动力学（CFD）方法进行了研究，以研究低流量自然循环条件下的NPP离心泵的流动行为。由于泵结构可能会根据流向导致不同的流量，因此建立了一个实验回路来测量不同流向的停止泵的压降和损耗系数。实验结果表明，在相同的雷诺数下，反方向的压降明显大于正方向的压降。此外，当雷诺数大于8×10时，损耗系数略有变化⁴; 然而，在较低的雷诺数条件下，系数随雷诺数的减少而迅速增加。根据实验数据，获得了泵损耗系数的经验相关性。还进行了CFD分析以模拟实验。仿真结果与实验结果吻合良好。此外，获得内部流场分布。可以看出，泵中主要部件的界面区域是造成最大压力损失的原因。在正向和反向条件之间的流场中也观察到显着差异。注意，本地流量随雷诺数不同而变化。研究表明，实验方法和CFD方法有助于增进对泵内部流动行为的了解。