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Research Papers: Multiphase Flows

Analysis of the Staggered and Fixed Cavitation Phenomenon Observed in Centrifugal Pumps Employing a Gap Drainage Impeller

[+] Author and Article Information
Bing Zhu

School of Energy and Power Engineering,
University of Shanghai for
Science and Technology,
Shanghai 200093, China
e-mail: zbing@usst.edu.cn

Hongxun Chen

Shanghai Institute of Applied
Mathematics and Mechanics,
Shanghai University,
Shanghai 200072, China
e-mail: chenhx@shu.edu.cn

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 11, 2016; final manuscript received October 3, 2016; published online January 19, 2017. Assoc. Editor: Matevz Dular.

J. Fluids Eng 139(3), 031301 (Jan 19, 2017) (11 pages) Paper No: FE-16-1229; doi: 10.1115/1.4034952 History: Received April 11, 2016; Revised October 03, 2016

Previous work has shown that the employment of a gap drainage impeller in a centrifugal pump can improve the pump's hydraulic performance and cavitation resistance. However, during experiments, an unconventional cavitation phenomenon has been observed in the form of a staggered pair of fixed impeller flow tunnels. For the purpose of understanding the factors involved with this unconventional phenomenon, the present study analyzes the cavitation formation and evolution processes using numerical and experimental methods. A scalable detached eddy simulation (SDES) method was employed to address unsteady turbulent flow. First, the method was validated by comparing the performance data and liquid water velocity distributions obtained by calculation and experiment in the absence of cavitation. Then, numerical simulations of the cavitation flow field were conducted under a flow discharge condition one-half that of the optimum value. Within a particular range of cavitation numbers, the calculated results are found to reproduce the unconventional cavitation phenomenon observed in the experiments. The formation mechanism involves a combination of many factors such as impeller geometry, inflow discharge condition, and cavitation number. As for a certain geometry, the formation and evolution processes can generally be analyzed and explained according to the influence of the attack angle, which is affected by variations in the allocated flow discharge and cavitation volume in each impeller tunnel. The jet flow through the gap between the main and vice blades also contributes to the formation of this phenomenon.

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Figures

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Fig. 2

Experimental setup for cavitation visualization

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Fig. 1

Experimental centrifugal pump test rig

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Fig. 3

Schematic representation of the physical pump including the gap drainage impeller (a) and the computational region (b)

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Fig. 4

Grid distributions: (a) global mesh and (b) impeller mesh

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Fig. 5

Comparison of the predicted hydraulic performance with that of the experimental data given according to the water head coefficient ψ and the efficiency η with respect to the pump flow discharge coefficient φ

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Fig. 6

Comparisons of the predicted average velocity distributions with PIV data for flow rates 0.5Q (top), Q (middle), and 1.5Q (bottom): (a) PIV and (b) CFD

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Fig. 7

Cavitation evolution with time (T5 = 5/3000 s, flow rate 0.5Q, and cavitation number σ = 0.42): (top) by high-speed camera and (bottom) by PIV camera

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Fig. 8

Comparison of the predicted performance with that of the experimentally obtained according to the water head coefficient ψ with respect to the cavitation number σ

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Fig. 10

Velocity distribution and water vapor volume fraction (σ=0.37, 5TB, and 0.5Q): (a) global velocity, (b) water vapor volume fraction, and (c) local velocity at the blade-to-blade plane

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Fig. 11

Cavitation evolution with respect to the cavitation number at the locked phase location (4.1TB): (a) water vapor volume fractions and (b) liquid water velocity streamline distributions

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Fig. 9

Circumferential evolution of cavitation at σ=0.37 with respect to time intervals TB = 60/(4 × 1000) s: (a) water vapor volume fraction distributions and (b) liquid water velocity streamline distributions

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