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Research Papers: Flows in Complex Systems

Numerical and Experimental Investigation of Tip Leakage Vortex Cavitation Patterns and Mechanisms in an Axial Flow Pump

[+] Author and Article Information
Desheng Zhang

Research Center of Fluid Machinery
Engineering and Technology,
Jiangsu University,
Zhenjiang 212013, China
e-mail: zds@ujs.edu.cn

Weidong Shi

Research Center of Fluid Machinery
Engineering and Technology,
Jiangsu University,
Zhenjiang 212013, China
e-mail: wdshi@ujs.edu.cn

Dazhi Pan

Research Center of Fluid Machinery
Engineering and Technology,
Jiangsu University,
Zhenjiang 212013, China
e-mail: 273729784@qq.com

Michel Dubuisson

Department of Mechanical Engineering,
Eindhoven University of Technology,
Eindhoven 5612 AZ, The Netherlands
e-mail: micdub@gmail.com

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 30, 2014; final manuscript received June 20, 2015; published online August 4, 2015. Assoc. Editor: Satoshi Watanabe.

J. Fluids Eng 137(12), 121103 (Aug 04, 2015) Paper No: FE-14-1544; doi: 10.1115/1.4030914 History: Received September 30, 2014

The tip leakage vortex (TLV) cavitating flow in an axial flow pump was simulated based on an improved shear stress transport (SST) k-ω turbulence model and the homogeneous cavitation model. The generation and dynamics of the TLV cavitation throughout the blade cascades at different cavitation numbers were investigated by the numerical and experimental visualizations. The investigation results show that the corner vortex cavitation in the tip clearance is correlated with the reversed flow at the pressure side (PS) corner of blade, and TLV shear layer cavitation is caused by the interaction between the wall jet flow in the tip and the main flow in the impeller. The TLV cavitation patterns including TLV cavitation, tip corner vortex cavitation, shear layer cavitation, and blowing cavitation are merged into the unstable large-scale TLV cloud cavitation at critical cavitation conditions, which grows and collapses periodically near trailing edge (TE).

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Pump geometry: (a) hydraulic components, (b) impeller blade geometry, and (c) guide vane geometry

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Fig. 2

Mesh of the axial flow pump: (a) computational zone, (b) surface mesh of main components, (c) refined mesh near tip, and (d) mesh near the blade surface

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Fig. 3

Distribution of y+ on the surface of blades and casing wall: (a) PS, (b) SS, and (c) casing wall

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Fig. 4

Schematics and overall dimensions of the axial flow pump loop: (a) side view and (b) top view

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Fig. 5

View of the axial flow pump model: (a) cross section of the model pump and (b) investigated axial flow pump

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Fig. 6

High-speed imaging system setup

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Fig. 7

Comparisons of (a) Φ–Ψ and (b) Ψ–σ curves

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Fig. 8

Comparison of numerical and experimental tip cavitation types, Q/QBEP = 1.0. Left: cavity isosurface av = 0.1 and right: experimental imaging of cavity. (a) σ = 0.558, (b) σ = 0.504, (c) σ = 0.481, (d) σ = 0.437, (e) σ = 0.415, and (f) σ = 0.349.

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Fig. 9

TLV cavitation inception (Q/QBEP = 1.0 and σ = 0.558)

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Fig. 10

Tip clearance cavitation, Q/QBEP = 1.0: (a) σ = 0.558 and (b) σ = 0.504

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Fig. 11

Structure of TLV cavitation, Q/QBEP = 1.0 and σ = 0.481: (a) TLV streamlines [33] and (b) isosurface of av = 0.1 (left) and visualization results (right)

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Fig. 12

Periodic TLV cloud cavitation at σ = 0.262. Experimental visualization of TLV cloud cavitation (T = 18 ms).

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Fig. 13

Blade tip parameters definition: (a) blade chord fraction λ and (b) blade thickness fraction δ

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Fig. 14

In-plane vapor fraction and static pressure distributions with velocity vectors. Q/QBEP = 1.0 and σ = 0.481. (a) λ = 0.2: 1—vapor fraction distribution with velocity vectors, 2—pressure distribution with velocity vectors, 3—partial view of tip near PS (vapor fraction and velocity vectors), and 4—partial view of tip near SS (vapor fraction and velocity vectors); (b) λ = 0.4: 1—vapor fraction distribution with velocity vectors, 2—pressure distribution with velocity vectors, 3—partial view of tip near PS (vapor fraction and velocity vectors), and 4—partial view of tip near SS (vapor fraction and velocity vectors); and (c) λ = 0.8: 1—vapor fraction distribution with velocity vectors, 2—pressure distribution with velocity vectors, 3—partial view of tip near PS (vapor fraction and velocity vectors), and 4—partial view of tip near SS (vapor fraction and velocity vectors).

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Fig. 15

Radial distributions of time-averaged axial velocity and TKE in the tip clearance, Q/QBEP = 1.0 and σ = 0.481: (a) axial velocity, λ = 0.5, (b) TKE, λ = 0.5, (c) axial velocity, λ = 0.8, and (d) TKE, λ = 0.8

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