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Research Papers

A Numerical Study of the Unsteady Interaction Effects on Diffuser Performance in a Centrifugal Compressor

[+] Author and Article Information
S. Anish

Fluid Machinery Technology
and Research Centre,
Daejoo Machinery Co. Ltd.,
1028 Wolam-dong, Dalseo,
Daegu 704-833, South Koreae-mail: anish.surendran@gmail.com

N. Sitaram

Professor
Department of Mechanical Engineering,
Indian Institute of Technology Madras,
Chennai 600-036, Tamil Nadu, India
e-mail: nsitaram@iitm.ac.in

H. D. Kim

Professor
School of Mechanical Engineering,
Andong National University,
388 Songchun-Dong, Andong,
Gyeongbuk 760-749, South Koreae-mail: kimhd@andong.ac.kr

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 29, 2012; final manuscript received December 23, 2012; published online September 23, 2013 Editor: David Wisler.

J. Turbomach 136(1), 011012 (Sep 23, 2013) (10 pages) Paper No: TURBO-12-1227; doi: 10.1115/1.4023471 History: Received November 29, 2012; Revised December 23, 2012

Interaction between rotating impeller and stationary diffuser in a centrifugal compressor is of practical importance in evaluating system performance. The present study aims at investigating how the interaction influences the unsteady diffuser performance and understanding the physical phenomena in the centrifugal compressor. A computational fluid dynamics (CFD) method has been applied to predict the flow field in the compressor, which has a conventional vaned diffuser (VD) and a low solidity vaned diffuser (LSVD). The radial gaps between impeller and diffuser and different flow coefficients are varied. The results obtained show that the major parameter that influences the unsteady variation of diffuser performance is due to the circumferential variation of the flow angle at the diffuser vane leading edge. The physical phenomena behind the pressure recovery variation are identified as the unsteady vortex shedding and the associated energy losses. The vortex core region as well as the shedding of vortices from the diffuser vane are triggered by the variation in the diffuser vane loading, which in turn is influenced by the circumferential variation of the impeller wake region. There is little unsteady variation of flow angle in the span-wise direction. This indicates that the steady state performance characteristics are related to the span-wise variation of flow angle, while the unsteady characteristics are contributed by the circumferential variation of flow angle. At design conditions, dominant frequency components of pressure fluctuation are all periodic and at near stall, these are aperiodic.

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References

Figures

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Fig. 4

Pressure coefficient contours at the diffuser wall (comparison expt. with CFD)

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Fig. 3

Solution dependency on the time step, for VD configuration

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Fig. 2

Computational mesh for VD configuration

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Fig. 5

Transient variation of the mass averaged total to static pressure ratio: (a) R3 = 1.05, VD (b) R3 = 1.10, VD (c) R3 = 1.05, LSVD, and (d) R3 = 1.10, LSVD

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Fig. 6

Variation of cp and ψ¯¯loss at different flow coefficients (VD and R3 = 1.05)

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Fig. 7

Variation of cp and ψ¯¯loss at different flow coefficients (VD and R3 = 1.15)

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Fig. 8

Variation of cp and ψ¯¯loss at different flow coefficients (LSVD and R3 = 1.05)

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Fig. 9

Variation of cp and ψ¯¯loss at different flow coefficients (LSVD and R3 = 1.15)

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Fig. 10

Total pressure contours at midspan (VD, R3 = 1.05 and ϕ = 0.23)

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Fig. 11

Total pressure contours at midspan (LSVD, R3 = 1.05 and ϕ = 0.23)

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Fig. 16

Variation in the diffuser vane loading at midspan for different R3 values for VD

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Fig. 17

Circumferential variation of flow angle at the vane leading edge (VD and ϕ = 0.23)

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Fig. 12

Vortex core region within the diffuser passage (LSVD, R3 = 1.10 and ϕ = 0.23)

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Fig. 13

Limiting streaklines at the lower vane surface showing the vortex core region (LSVD, R3 = 1.10 and ϕ = 0.23)

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Fig. 14

Vortex core region within the diffuser passage (LSVD, R3 = 1.10 and ϕ = 0.60)

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Fig. 15

Diffuser vane loading at different time steps for LSVD; R3 = 1.10; ϕ = 0.23

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Fig. 20

Power spectral density (PSD) distributions of the static pressure fluctuations (LSVD, R3 = 1.10 and ϕ = 0.34)

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Fig. 21

Power spectral density (PSD) distributions of the static pressure fluctuations (LSVD, R3 = 1.10 and ϕ = 0.23)

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Fig. 1

Schematic views of centrifugal compressors with different types of diffusers

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Fig. 18

Span-wise variation of incidence angle (VD and R3 = 1.05)

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Fig. 19

Span-wise variation of incidence angle (VD and R3 = 1.15)

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Fig. 22

Power spectral density (PSD) distributions of the static pressure fluctuations (VD, R3 = 1.10 and ϕ = 0.34)

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