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Flows in Complex Systems

Low Field in the Vaned Diffuser of a Centrifugal Pump at Different Vane Setting Angles

[+] Author and Article Information
P. Gaetani

Dipartimento di Energia, Politecnico di Milano, Via Lambruschini, 4, 20158 Milano, Italypaolo.gaetani@polimi.it

A. Boccazzi

CNR – IENI, Via Lambruschini, 4, 20158 Milano, Italyaldo.boccazzi@polimi.it

R. Sala

 Dip. Ing. Idraulica e AmbientaleUniversità di PaviaVia Ferrata, 127100, Pavia, Italyrsala@unipv.it

J. Fluids Eng 134(3), 031101 (Mar 19, 2012) (12 pages) doi:10.1115/1.4005902 History: Received September 16, 2011; Revised January 23, 2012; Published March 16, 2012; Online March 19, 2012

Particle image velocimetry (2D-PIV) has been used for the investigation of the time and phase-averaged flow field inside the vaned diffuser of a centrifugal pump operating at the best efficiency point (BEP). Pump performances and the diffuser flow field were analyzed for three different vane setting angles. It was evidenced that flow coefficient at the best efficiency point decreases with the diffuser setting angle reduction. From 2D-PIV measurements in five different blade to blade planes, spanwise averaged flow angles and velocity distribution were computed. It was evidenced an influence of the diffuser setting angle on the spanwise distribution of the flow rate and of the absolute mass averaged flow angle at impeller discharge. An overturning at the diffuser discharge was also evidenced for the two highest setting angles. 2D-PIV flow fields are presented in three different pseudosecondary planes in order to enlighten the cross flows affecting the diffuser flow field.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Expanded view of the pump and reference to typical pump sections

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Figure 2

CCD field of view for diffuser D2. For one of the vanes, the different settings are shown.

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Figure 3

(a) Impeller discharge rake angle and (b) field of view for diffuser C.A.

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Figure 4

Pump performance curves

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Figure 5

BEP flow coefficient versus nondimensional diffuser throat area

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Figure 6

Time-averaged flow fields at different spans for diffuser D1; φ  =  φBEP . Contour plot colors show time-averaged velocities. Only one vector over two is shown for clarity.

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Figure 7

Time-averaged flow fields at midspan for different diffusers

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Figure 8

(a) Pitch-averaged radial and (b) tangential velocity components at the impeller discharge along the diffuser span for the different diffusers

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Figure 9

(a) Mass averaged absolute flow angle and (b) incidence at the impeller discharge along the diffuser span for the different diffusers

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Figure 10

(a) Pitch-averaged radial velocity component and (b) flow angle at the diffuser trailing edge

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Figure 11

Relative and absolute mass averaged flow angles at (a) impeller discharge and (b) incidence angle at diffuser inlet for different diffuser

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Figure 12

Geometrical and mass averaged flow angles at (a) diffuser discharge and (b) flow deflections for different diffusers

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Figure 13

Spanwise time-averaged velocity component (positive toward the shroud) in pseudosecondary planes. Vectors components are δu [Eq. 4] and ⟨⟨v⟩⟩. The vane trailing edge trace is evidenced by a black line.

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Figure 14

Phase-averaged flow fields for diffuser D2 at φ  =  φBEP . Contour plot colors show phase-averaged velocities. Only one vector over two is shown for clarity.

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Figure 15

Phase-averaged flow fields in the blade to blade plane at (a) midspan and (b) in the pseudosecondary plane A. Vectors show the cyclic velocity fluctuation: δV→ [Eq. 5].

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Figure 16

(a), (c) Time-averaged flow field and (b), (d) vorticity for diffuser D2 at (a), (b) φBEP and at (c), (d) 0.6 φBEP

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Figure 17

Phase-averaged flow angle (α) and stream traces for diffuser D3 at midspan for different impeller phase angles ϕ (0 deg to 50 deg, 10 deg step)

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