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Purpose – The purpose of this paper is to elucidate the detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition. Design/methodology/approach – Unsteady flows in a centrifugal pump volute at non-cavitation and cavitation conditions are investigated by using a computation fluid dynamics framework combining the re-normalization group k-e turbulence model and the mass transport cavitation model. Findings – The flow field in pump volute is very complicated at part load condition with large pressure gradient and intensive vortex movement. Under cavitation conditions, the dominant frequency for most of the monitoring points in volute transit from the blade passing frequency to a lower frequency. Generally, the maximum amplitudes of pressure fluctuations in volute at serious cavitation condition is twice than that at non-cavitation condition because of the violent disturbances caused by cavitation shedding and explosion. Originality/value – The detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition are revealed and analysed.

Tip clearance between blade end and shroud is inevitable in pump operation and of great importance on pump energy performance and pressure fluctuation. As the tip clearance size increases, the head and efficiency of the mixed flow pump drop accordingly. The simulation results show that the development of a leakage vortex is observed as the tip clearance increases, and the trajectory of this leakage vortex remains in the same direction along the blade suction side for different tip clearances. With the increase in tip clearance size, the intensity of the leakage vortex is enhanced, and the separation between the main leakage vortex and the secondary leakage vortex is also strengthened. The leakage separation angle near the blade tip remains at the same value of 10° for different tip clearance sizes. As for the spectrum analysis, the maximum amplitudes of pressure fluctuations dramatically increase in the impeller when the tip clearance increases from 0.0 mm to 1.0 mm, and the dominant frequencies go from 145 Hz to 184 Hz due to the considerable leakage flow.

Abstract:The influence of prewhirl regulation by inlet guide vanes (IGVs) on a centrifugal pump performance is investigated experimentally and numerically. The experimental results show that IGVs can obviously change the head and increase the efficiency of the tested centrifugal pump over a wide range of flow rates. Although the cavitation performance is degraded, the variation of the cavitation critical point is less than 0.5 m. Movement of the computed three-dimensional streamlines in suction pipe and impeller are analyzed in order to reveal the mechanism how the IGVs realize the prewhirl regulation. The calculated results show that the influence of IGVs on the cavitation performance of centrifugal pump is limited by a maximum total pressure drop of 1777 Pa, about 7.6% of the total pressure at the suction pipe inlet for a prewhirl angle of 24°.

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Prewhirl regulation by inlet guide vanes (IGVs) has been proven as an effective method for operation regulation of centrifugal pumps. By contrast, the influence of the geometry of IGVs on operation stability of centrifugal pump remains unknown. The pressure fluctuations and flow patterns in a centrifugal pump without and with two-dimensional (2D) or three-dimensional (3D) IGVs are investigated numerically at 1.0Qd, 0.6Qd, and 1.2Qd. Renormalization group (RNG) k–ε turbulence model is used as turbulence model, and fast Fourier transform (FFT) method is used to analyze the pressure fluctuations. The dominant frequency of pressure fluctuations in impellers is either the rotational frequency fi or twice thereof for pumps without and with IGVs at three flow rates, while the dominant frequency is constantly the blade passing frequency in volute. For 1.0Qd, the comparison of pumps without IGVs indicates that the maximum amplitude of pressure fluctuations at fi in pumps with 2D IGVs is decreased by an average of 22.2%, and the amplitude is decreased by an average of 44.9% in pumps with 3D IGVs. The IGVs mainly influence the pressure fluctuations at fi but indicate minimal influence at 2fi. For 0.6Qd, the comparison of pumps without IGVs denotes that the maximum amplitudes of pressure fluctuations at fi in pumps with 2D or 3D IGVs both increase; the maximum increase is 2.01%. For 1.2Qd, the comparison of pumps without IGVs indicates that the maximum amplitudes of pressure fluctuations at fi in pumps with 2D or 3D IGVs both decrease; the maximum decline is 15.9%.