非均匀入流对CAP1400核主泵内流及性能的影响研究

Effect of Non-Uniform Inflow on the Internal Flow and Performance of the Reactor Coolant Pump in CAP1400 System

针对CAP1400反应堆冷却剂系统中,由于蒸发器下腔室和核主泵直接相连导致核主泵入口产生非均匀入流,从而影响核主泵内部流场的问题,通过基于剪切应力运输模型的全三维CFD模拟方法,对蒸发器下腔室和核主泵联合模型进行数值模拟,分析了蒸发器下腔室致非均匀流动的形成机理,研究了非均匀入流对核主泵内部流动和水力性能的影响。结果表明:下腔室非对称结构和突缩截面的流动分离是非均匀流动的主要成因。在额定工况下,非均匀入流导致左侧和右侧核主泵扬程分别下降6.0%、5.1%,效率分别下降7.2%、6.6%;在0.5~1.2倍额定流量工况范围内,性能下降幅度与流量呈正相关。非均匀入流呈现轴向速度分布不均匀并伴随二次流动的稳定结构,并且左右两侧叶轮内非均匀入流的旋流畸变特性和轴向速度分布不同。叶轮入口旋流畸变引起入口冲角发生变化,与均匀入流相比,左右两侧叶轮叶高中部的冲角变化相反,而叶顶部分冲角均增加、叶根部分冲角均减小;叶轮入口轴向速度不均匀引起左右两侧叶轮各流道的流量波动分别增大3倍和2倍,降低了核主泵的运行稳定性。

In CAP1400 reactor coolant system,because the lower header of steam generator and the reactor coolant pump are directly connected,non-uniform inflow is generated at the pump inlet and impacts the internal flow of the pump.By full-scale three-dimensional CFD simulation based on shear stress transport model,numerical calculation of the lower header-pump combined model is conducted to analyze the formation mechanism of non-uniform inflow in the lower header of steam generator and investigate the effect of non-uniform inflow on the internal flow and hydraulic performance of the pump.The results show that non-uniform inflow is mainly caused by the asymmetric structure of the lower header and the flow separation at suddenly reduced section.Under the design flow rate conditions,the non-uniform inflow leads to a 6.0%and 5.1%decrease in head and a 7.2%and 6.6%decrease in efficiency for the left and right pumps,respectively.Under the condition of 0.5 to 1.2 times design flow rate,the performance decrease is positively correlated with flow rate.In addition,non-uniform inflow presents a stable structure with uneven axial velocity distribution and secondary flow,and the inflows of the left and right impellers have different swirl distortion characteristics and axial velocity distribution.The swirl distortion at the impeller inlet causes changes in the inlet impulse angle.Compared with uniform inflow,the impulse angle in the middle of the blade of the left and right impellers changes in the opposite direction,while the impulse angle at the blade top increases and the angle at the blade root decreases.The flow fluctuations in the flow channels of the left and right impellers increase by three times and twice respectively due to the uneven axial velocity at the impeller inlet,leading to degraded operational stability of the reactor coolant pump.