低比转数离心泵小流量工况下的压力脉动特性

为了研究低比转数离心泵在小流量下的压力脉动特性,以IS50-32-160型离心泵为研究对象,在对模型泵进行网格无关性分析的基础上,采用分离涡模拟对不同小流量工况下的内部非定常流动进行数值计算.计算结果表明:隔舌对叶轮内部流动的影响较大,靠近隔舌的3个流道内均存在不同程度的进、出口旋涡,进口旋涡从叶片吸力面处产生,方向与叶轮旋转方向相同,而出口旋涡在叶片压力面产生,方向与叶轮旋转方向相同;随着流量的减小,旋涡不断发展,尤其是隔舌所在流道,进、出口旋涡会堵塞整个流道,且蜗壳出口会出现流动分离,导致出流不均匀;对叶轮和蜗壳内各监测点进行快速傅里叶变换,发现叶轮内的主要脉动频率为轴频及其倍频,且脉动从吸力面到压力面、进口到出口均逐渐增大;蜗壳内主要脉动频率为叶频及其倍频,且越靠近隔舌脉动越大,在隔舌处达到极大值;各监测点的脉动强度随流量的减小而增强.

Pressure fluctuation characteristics of centrifugal pump with low-specific speed at low flow rate

In order to investigate into the internal unsteady flow of low specific speed centrifugal pump at various low flow rates, a series of numerical simulations of DES(detached eddy simulation)in an end-suction centrifugal pump of type IS50-32-160 are carried out on the basis of analysis on grid independence. The results show that the tongue has a more important influence on the internal flow in the impeller, causing different size vortices exist in three flow passages near the tongue; the vortices just behind the impeller inlet are close the blade suction side with the same rotation direction as the impeller, but the vortexes near the impeller outlet are in front of the blade pressure side in the reverse direction of the impeller. With declining flow rate the vortexes expand so fast that even block the whole passage, especially in the three passages near the tongue. Meanwhile, a flow separation emerges in the volute nozzle, resulting in a non-uniform outflow. A FFT(fast Fourier transformation)frequency transformation is conducted for the pressure signals picked up at the monitoring points in the impeller and volute, and it is found out that the dominated frequencies in the impeller are the shaft frequency and its integer multiples, and the amplitude of pressure pulsation increases steadily with the radius and from the suction side to the pressure side. In contrast, the dominated frequencies in the volute are the blade frequency and its integer multiples, the more violent the amplitude of pressure pulsation, the smaller the distance to the tongue, eventually, the greatest pulsation occurs on the tongue. The intensity of pressure pulsation at all the monitoring points gets stronger with decreasing flow rate.