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Research Papers: Flows in Complex Systems

Numerical Investigation of Back Vane Design and Its Impact on Pump Performance

[+] Author and Article Information
Farzam Mortazavi

Mem. ASME
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843-3123
e-mail: farzam.mortazavi@tamu.edu

Alireza Riasi

Department of Mechanical Engineering,
University of Tehran,
Tehran 11155-4563, Iran
e-mail: ariasi@ut.ac.ir

Ahmad Nourbakhsh

Professor
Hydraulic Machinery Research Institute,
University of Tehran,
Tehran 11155-4563, Iran
e-mail: anour@ut.ac.ir

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 29, 2017; final manuscript received July 2, 2017; published online September 1, 2017. Assoc. Editor: Ioannis K. Nikolos.

J. Fluids Eng 139(12), 121104 (Sep 01, 2017) (9 pages) Paper No: FE-17-1196; doi: 10.1115/1.4037281 History: Received March 29, 2017; Revised July 02, 2017

Adding back vanes to the rear shroud of centrifugal pumps is sometimes practiced in order to alleviate large axial forces. Effective design and flow characteristics of back vanes remain obscure due to lack of knowledge associated with experimental complexities in study of this area. In this study, various design parameters of the conventional noncurved rectangular back vanes are evaluated using computational fluid dynamics (CFD). Furthermore, the complex flow structure at the rear chamber of these pumps is illustrated and discussed with the advantage of CFD which is a highly costly and taxing job if one chooses to capture it using experimental methods. Effect of back vanes outer radius, width, clearance, thickness, vane angle, and number of vanes on pump characteristics and axial thrust has been investigated. New findings of this study show that back vanes are capable of canceling the axial thrust in a large range of flow rates without a penalty to the machine efficiency, provided that suitable design parameters are selected. In addition, the best efficiency point (BEP) will not be affected by usage of back vanes. The rear chamber’s flow pattern suggest that back vanes have a repumping effect causing increased pump head at longer back vane configurations.

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Figures

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Fig. 1

Axial thrust canceled by back vanes

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Fig. 2

Back vane design parameters

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Fig. 3

Grid density for various grid cell sizes. The selected grid of 5.2 × 106 cells has 20 layers of mesh across the clearance.

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Fig. 4

Computational domains and the structured grid

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Fig. 5

y+ values contoured for the primary and rear passages

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Fig. 7

Grid independency results

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Fig. 8

Comparison of streamlines and velocity vectors at the sample planes z¯=0.05 and θ=0 for the selected grid and the finest grid

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Fig. 9

Pressure distribution and streamlines in the rotating frame sampled at three axial planes

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Fig. 10

Velocity field at sample radial planes

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Fig. 11

Swirl ratio distribution inside rear chamber sampled at three axial planes

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Fig. 12

Circumferentially averaged swirl ratio profiles at various radial positions

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Fig. 13

Circumferentially averaged radial velocity profiles at various radial positions

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Fig. 14

Impeller and pump head variation with and without back vanes

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Fig. 15

Axial thrust variation with and without back vanes

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Fig. 16

Pump efficiency variation with and without back vanes

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Fig. 17

Power consumption with and without back vanes

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Fig. 18

Disk power loss efficiency with and without back vanes

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Fig. 19

Swirl ratio (volume averaged) variation with and without back vanes

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Fig. 20

Design parameters effect on axial thrust

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Fig. 21

Design parameters effect on the pump head

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Fig. 22

Design parameter effect on the pump efficiency

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Fig. 23

Number of vanes effect on the pump efficiency, head, and axial thrust

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