余热排出泵内部不稳定流动数值模拟与实验研究

Numerical and experimental study on flow instabilities in residual heat removal pumps

为了研究余热排出泵在多工况下内部流动特性,基于ANSYS CFX软件,采用SST湍流模型,对模型泵进行三维非定常数值模拟,获得了不同工况下余热排出泵的水力性能、内部流场结构和压力脉动特性,同时展开压力脉动实验研究,并与计算结果进行对比。研究结果表明:大流量(1.2Q_d)和设计流量(1.0Q_d)工况下,叶轮和导叶内部流动比较稳定,随着流量的减小叶片进口背面附近开始形成失速旋涡,流道内均发生不同程度的流动分离,且沿着流道向出口处发展;叶轮出口压力脉动主频为7f_z,受导叶叶片数影响;导叶和蜗壳出口的主频均为5f_z,主要由叶频决定;设计流量下各监测点处压力脉动系数幅值最小,越往小流量工况,幅值越大;说明在小流量工况下余热排出泵内部出现了不稳定流动现象。

In order to investigate the flow characteristics of residual heat removal pumps under multi conditions,three-dimensional unsteady numerical simulations were conducted by using the SST turbulence model in ANSYS CFX. The performance,inner flow fields,and pressure fluctuation of the residual heat removal pumps under multi conditions was obtained and compared with experimental results. The results show that： the inner flow keep regular under 1. 2Q_d and 1. 0Q_d. However,with the decrease of the flow rate,the stall vortex generates near the suction side at the impeller and diffuser inlet associated with the onset of varying degrees of flow separation in the flow channels,which is intensified toward the outlet. The main frequency of pressure fluctuation at the outlet of the impeller affected by the number of vanes is 7f_z. The main frequencies at the outlet of both the diffuser and volute is 5f_z,which are the blade passing frequency. The amplitudes of fluctuating pressure coefficient in all the monitoring points reach its minimum value under design condition,which increase gradually with the decrease of flow rate. It is concluded that the flow instabilities inside the pump occurs under small flow rate condition.