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Research Papers: Flows in Complex Systems

Numerical and Experimental Analysis of Flow Phenomena in a Centrifugal Pump Operating Under Low Flow Rates

[+] Author and Article Information
Yanxia Fu

National Research Center of Pumps,
Jiangsu University,
Zhenjiang 212013, China;
Civil and Industrial Engineering Department,
University of Pisa,
2 Largo L. Lazzarino, Pisa 56121, Italy
e-mail: yanxiafu40@gmail.com

Jianping Yuan

Professor
National Research Center of Pumps,
Jiangsu University,
Zhenjiang 212013, China
e-mail: yh@ujs.edu.cn

Shouqi Yuan

Professor
National Research Center of Pumps,
Jiangsu University,
Zhenjiang 212013, China
e-mail: shouqiy@ujs.edu.cn

Giovanni Pace

Civil and Industrial Engineering Department,
University of Pisa,
2 Largo L. Lazzarino, Pisa 56121, Italy
e-mail: giov.pace@gmail.com

Luca d'Agostino

Professor
Civil and Industrial Engineering Department,
University of Pisa,
2 Largo L. Lazzarino, Pisa 56121, Italy
e-mail: luca.dagostino@ing.unipi.it

Ping Huang

National Research Center of Pumps,
Jiangsu University,
Zhenjiang 212013, China
e-mail: Huangping@ujs.edu.cn

Xiaojun Li

National Research Center of Pumps,
Jiangsu University,
Zhenjiang 212013, China
e-mail: lixiaojun530@gmail.com

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 26, 2013; final manuscript received February 27, 2014; published online September 10, 2014. Assoc. Editor: Satoshi Watanabe.

J. Fluids Eng 137(1), 011102 (Sep 10, 2014) (12 pages) Paper No: FE-13-1639; doi: 10.1115/1.4027142 History: Received October 26, 2013; Revised February 27, 2014

The characteristics of flow instabilities as well as the cavitation phenomenon in a centrifugal pump operating at low flow rates were studied by experimental and numerical means, respectively. Specially, a three-dimensional (3D) numerical model of cavitation was applied to simulate the internal flow through the pump and suitably long portions of the inlet and outlet ducts. As expected, cavitation proved to occur over a wide range of low flow rates, producing a characteristic creeping shape of the head-drop curve and developing in the form of nonaxisymmetric cavities. As expected, the occurrence of these cavities, attached to the blade suction sides, was found to depend on the pump's flow coefficient and cavitation number. The experiments focused on the flow visualization of the internal flow patterns by means of high-speed digital movies and in the analysis of the inlet pressure pulsations near the impeller eye by means of fast response pressure transducers. The experimental results showed that the unsteady behavior of the internal flow in the centrifugal pump operating at low flow rates has the characteristics of a peculiar low-frequency oscillation. Meanwhile, under certain conditions, the low-frequency pressure fluctuations were closely correlated to the flow instabilities induced by the occurrence of cavitation phenomena at low flow rates. Finally, the hydraulic performances of the centrifugal pump predicted by numerical simulations were in good agreement with the corresponding experimental data.

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References

Figures

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Fig. 1

2D views of (a) impeller and (b) volute

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Fig. 2

Grids of the CFD model centrifugal pump

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Fig. 3

Velocity distributions on the midspan of the pump and blade loading at the design condition based on three different mesh numbers

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Fig. 4

(a) Head-drop curves and (b) the Q − σ3% curve of the centrifugal test pump

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Fig. 5

Variations of the parameter σ/2α under a function of the cavitation number σ at different flow coefficients: (a) 40% and (b) 50% of the design flow rate. The values of σ/2α corresponding to the onset of cavitation impact on head are shown in red.

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Fig. 6

Static pressure distribution in the midspan of the pump under different flow rates

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Fig. 7

Vapor structures within the impeller cross sections at a flow coefficient equal to 40% of the design value for decreasing values of the inlet total pressure

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Fig. 8

Vapor structures within the impeller cross sections at a flow coefficient equal to 120% of the design value for decreasing values of the inlet total pressure

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Fig. 9

Vapor structures in the test pump at Q/Qd = 0.4 as the inlet total pressure decreases

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Fig. 10

Vapor structures in the test pump at Q/Qd = 1.2 as the inlet total pressure decreases

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Fig. 11

Layout of the test facilities for (a) pump hydraulic performances and (b) the visualization test

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Fig. 12

The centrifugal pump tested in (a) the experiments and (b) the transparent Plexiglas inlet pipe of the test pump and the Y-series 4 L; (c) High-speed camera used in the experiments and (d) the digital acquisition systems of the unsteady pressure signals

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Fig. 13

Hydraulic performances of the test centrifugal pump

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Fig. 14

Visualizations of vapor structures in inlet pipe under the flow rate Q/Qd = 0.1 at different subsequent time

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Fig. 15

Frequency domain of power spectral density of the pressure fluctuation based on the voltage signals from pressure transducers in a pump inlet pipe

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