不同叶轮形式离心泵压力脉动和空化特性试验研究

Experimental investigation of pressure fluctuation and cavitation for a centrifugal pump with different impeller configurations

压力脉动和空化特性是影响离心泵稳定运行的两个重要因素。针对国内某大型调水工程的立式带导叶离心泵,在保证蜗壳、导叶和叶轮出口直径等设计参数一致的情况下,设计了两种不同形式的模型叶轮,并进行了模型泵的同台试验。两个叶轮的比转速都为106.43,叶片数分别为7和9,叶轮流道、叶型也不相同,其中,对9叶片叶轮叶片进口边进行了"C形"修型。结果表明,两种叶轮形式离心泵内部压力脉动的频率成分及其分布特性类似,总体上都为叶片通过频率及其谐频,且该频率的压力脉动能通过叶轮流道逆水流方向向进口端传播。叶轮形式对压力脉动幅值的影响比较显著,相比7叶片叶轮,9叶片叶轮的压力脉动幅值降低了10%以上。同时,对叶片进口边修型后,初生空化得到有效延迟,设计流量点附近的临界空化余量下降约10%。适当提高叶片数与叶片进口边修型可显著提高离心泵空化性能。

The pressure fluctuation and cavitation characteristics are two important factors that affect the op- eration stability of centrifugal pumps. According to the large vertical centrifugal pump for a large domestic water replenishment project, two impeller models were designed with main design parameters unchanged such as the volute, vane diffuser and impeller outlet diameter. The experiments were carried out on the same test rig. The specific speeds of the impeller were both 106.43, while the blade numbers were 7 and 9 respectively. The shapes of flow passage and blade were different, and the leading edge of the blade of the impeller with 9 blades was modified by ＂C＂ cut. The results show that the frequency components and distribution of pressure fluctuations are similar for the investigated two impeller configurations, and the main frequencies of pressure fluctuations are the blade passage frequency and its harmonic frequency. Such components of the pressure fluctuation could spread through against the flow direction to the impeller inlet. The differences are reflected on the amplitude of the pressure fluctuations. Comparing with the impeller with 7 blades, the amplitude of pressure fluctuation in the pump with 9 blades decreases at least 10%. Ap- propriate modifications on the blade leading edge could effectively delay the occurrence of the incipient cavi- tation, and the value of critical NPSH could decrease 10% at the design flow rate. Thus, a proper in- crease of the blade number and reasonable modification of the blade leading edge could improve the cavita- tion performance.