Abstract
In order to investigate the mechanism and the characteristics of the noise induced by unstable flow in a centrifugal pump, the internal flow characteristics in the pump were numerically researched, and the acoustic pressure fluctuations at the pump inlet and outlet were experimentally investigated. Obvious corresponding relationships between the flow instabilities, the cavitation and the noise were established. It was found that the rotating stall, the backflow, the hump, the occurrence of unstable flow and the cavitation in such a centrifugal pump were effectively detected through the noise, which could help to provide fundamental information on flow instabilities and guarantee safe and steady operating conditions for the system. The recirculation and prewhirl regions in the pump upstream pipe, which were caused by the backflow and the rotation of the impeller, presented the circumferential movement with a spiral shape, causing apparent broadband fluctuations at low frequency band of the acoustic pressure. The backflow and rotating stall could also result in broadband fluctuations of the pump outlet noise, which was distributed from 100 Hz to 150 Hz. Meanwhile, the broadband fluctuations of the pump outlet acoustic pressure distributed in the low frequency range, which was produced by the occurrence of cavitation, moved to the lower frequency band as the flow rate increased. The enhanced broadband fluctuations of the pump inlet and outlet noise distributed from 1 kHz to 6 kHz were caused by the coupling between the cavitation-induced noise and the system-produced noise. The broadband fluctuations of the pump inlet noise distributed between 6 kHz and 9 kHz were regarded as the typical frequency band of cavitation in the centrifugal pump.
Highlights
Centrifugal pumps are widely applied in a variety of fields, such as industrial plants, agricultural irrigation, the petroleum and chemical industries, aeronautics and astronautics [1,2,3]
To establish establish the the relationship between the intensification of noise and the aggravation of flow instabilities, the streamlines relationship between the intensification of noise and the aggravation of flow instabilities, the of water velocity distributed in planes Ainand the centrifugal pump are pump illustrated in Figure in streamlines of water velocity distributed planes and
Due to the flow and the cavitation in such a centrifugal pump were effectively detected through the noise, which could help to provide fundamental information on flow instabilities and guarantee safe and steady operating conditions for the system
Summary
Centrifugal pumps are widely applied in a variety of fields, such as industrial plants, agricultural irrigation, the petroleum and chemical industries, aeronautics and astronautics [1,2,3]. Due to the current energy crisis and restrictions on environmental noise levels, centrifugal pumps that operate with low noise, high efficiency, high rotating speed and high reliability have become increasingly important. The unstable flow in centrifugal pumps results in pressure fluctuations at both the inlet and outlet [4,5] and accounts for the generation of noise [6,7]. The noise induced by unstable flow and cavitation are mainly caused by inducers and turbopumps, which have rather high rotation speeds [8,9]. The hydraulic noise caused by diffuser pumps and volute is theoretically investigated by Clark, who finds that the noise generated by the pump casing is weak, the blade wake and blade circulation are of prime
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