空化对超低比转数离心泵内压力脉动的影响研究

为研究空化对超低比转数离心泵内压力脉动的影响,采用实验和数值模拟相结合的方法,研究了IB 50-32-250型超低比转数离心泵在不同有效汽蚀余量下不同位置处的压力脉动,并对其频域和幅值特性进行了分析。结果表明:空化会诱导产生低频及宽频脉动。无空化时,叶轮流道内压力脉动主频为转频及其倍频,蜗壳内压力脉动受叶轮和隔舌间的相互作用激励,主频为叶频及其倍频,且与隔舌越近脉动越强。随着有效汽蚀余量的减小,叶轮通道中大部分测点的压力脉动幅值减小,但空化区边缘的脉动幅值增大;临界空化时,叶轮进口附近的压力脉动主频由转频变为1/6倍转频。此外,蜗壳内流场的不均匀变化导致蜗壳内压力脉动幅值增大;临界空化时,蜗壳及泵出口处的主频仍为叶频,但1/6倍转频成为幅值较大的次频。

Investigation on Pressure Fluctuation Affected by Cavitation in Ultra-low Specific Speed Centrifugal Pump

In order to investigate the influence of cavitation on pressure pulsation in ultra low specific speed centrifugal pump, combining experimental and numerical simulation methods, the frequency domain and amplitude characteristics of pressure fluctuation were analyzed at different positions in an IB 50-32-250 ultra low specific speed centrifugal pump with different net position suction head available (NPSHa). The results showed that cavitation can induce low frequency and broadband frequency fluctuation. When there was no cavitation, the pressure pulsation in impeller flow passage was mainly related to the impeller rotation frequency and its harmonic frequency;while in the volute, because of the interference between impeller and volute tongue, the main dominant frequency of pressure pulsation was the blade pass frequency and its harmonic frequency, and the pressure pulsation near tongue was the strongest. With the decrease of NPSHa, pressure fluctuation of most monitors in the impeller passage was weakened, but that in the edge of cavitation zone was enhanced. The main frequency of pressure pulsation near the impeller inlet was changed from rotation frequency to 1/6 rotation frequency at the critical cavitation. Besides, the developing un uniformity of flow field in volute caused the amplitude of pressure fluctuation strengthened. The main frequency of the volute and pump outlet was still blade pass frequency, but 1/6 rotation frequency became the secondary frequency with larger amplitude. The research can provide necessary basis for the reduction of vibration and noise intensified by cavitation in the ultra low specific speed centrifugal pump.