余热排出泵不同启动过程的内部流动特性

Internal flow characteristics of residual heat removal pump during different starting periods

为研究余热排出泵不同启动过程的内部流动演化过程,采用基于Flowmaster与CFD的联合仿真方法对余热排出泵3种启动过程内部瞬态流场进行了数值模拟,分析了不同启动过程泵内压力、速度分布规律以及叶轮和导叶流道内的旋涡演变过程.基于Matlab-Simulink建立电动机启动模型,通过仿真后得到电动机启动过程转速随时间变化规律,结果表明:电动机经过5.5 s后,达到额定转速;在Flowmaster中建立余热排出泵启动过程仿真模型,得到不同启动过程中的流量变化规律;分析不同启动过程余热排出泵内部流场,由于交替启动过程是在高温高压的工况下运行,泵内压力梯度要明显大于最小流量管线启动过程,而双泵运行状态时蜗壳内的压力分布基本保持不变;分析不同启动过程余热排出泵内部速度分布及旋涡演化规律,3种启动方式都经历了旋涡的产生、分离、消失3个不同阶段,双泵运行状态下旋涡消失要早于最小流量管线启动和交替启动过程,在t=5.5 s时流道内流动已相对均匀,直至稳定运行状态,由此反映了启动过程中流体的惯性作用明显影响着流场的发展;对比3种启动过程下扬程曲线,双泵运行状态时扬程最小,扬程随叶轮旋转达到最大值,并出现一个瞬时冲击扬程,双泵运行状态时冲击现象最为明显.

In order to investigate the evolution process of internal flow in residual heat removal pumps during different starting periods, the transient flow field in a residual heat removal pump is simulated by using a method based on the combination of Flowmaster and CFD technology, and the evolution processes of pressure, velocity and vortex in the impeller and guide vanes are analyzed. A mathematical model is built for the motor starting period with Matlab - Simulink, then the motor speed variation with time is obtained through a simulation, showing the rated speed can be achieved at 5.5 s. Further, a model is generated in Flowmaster to simulate the starting process of the residual heat removal pump,and the flow variations with time are obtained during different starting periods. Finally, the internal flow fields in the pump are analyzed in ANSYS CFX during different starting periods. It is shown that the pressure gradient is obviously sharper during the alternating starting period than during the minimum flow starting period in pipeline because the pump is subject to a high temperature and high pressure condition in the former period, while the pressure distribution in the volute almost remains unchanged in the dual-pump operating period. The vortex evolution processes in the impeller and guide vanes all experience three different stages, namely, vortex generation, separation and disappearance in three different starting periods. Note that the vortex disappears sooner during the dual-pump operating period than in the other two periods. The flow in the flow passages becomes uniform at 5.5 s, reflecting the inertia action of fluid affects the development of flow field in different starting periods significantly. The head is the minimum during the dual-pump operating period in comparison with the other periods, and the head rises with increasing impeller rotating speed with an overshoot as the speed stops accelerating. The overshoot effect is mostly evident during the dual-pump operating period.