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Research Papers

A Study on Matching Between Centrifugal Compressor Impeller and Low Solidity Diffuser and Its Extension to Vaneless Diffuser

[+] Author and Article Information
Hideaki Tamaki

Corporate Research & Development,
IHI Corporation,
1, Shin-Nakahara-Cho,
Isogo-Ku 235-8501, Yokohama, Japan
e-mail: hideaki_tamaki@ihi.co.jp

Manuscript received June 24, 2018; final manuscript received July 4, 2018; published online December 5, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(4), 041026 (Dec 05, 2018) (16 pages) Paper No: GTP-18-1331; doi: 10.1115/1.4041003 History: Received June 24, 2018; Revised July 04, 2018

A centrifugal compressor requires a wide operating range as well as a high efficiency. At high pressure ratios, the impeller discharge velocity becomes transonic and effective pressure recovery in a vaned or vaneless diffuser is necessary. At high pressure ratios, a vaned diffuser is used as it has high pressure recovery, but may have a narrow operating range. At low flow, diffuser stall may trigger surge. At high flow, choking in the throat of the vanes may limit the maximum flow rate. A low solidity diffuser allows a good pressure recovery because it has vanes to guide the flow and a wide operating range as there is no geometrical throat to limit the maximum flow. In experimental studies at a pressure ratio around 4:1, the author has replaced vaned diffusers with a range of low solidity diffusers to try to broaden the operating range. The test results showed that the low solidity diffuser also chokes. In this paper, a virtual throat is defined and its existence is confirmed by flow visualization and pressure measurements. A method to select low solidity diffusers is proposed based on test data and the fundamental nature of the flow. The extension of the proposed method to the selection of a vaneless diffuser is examined and a design approach for a vaneless diffuser system to minimize surge flow rate without limiting the attainable maximum flow rate is proposed.

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References

Tamaki, H. , 2015, “ Experimental Study on Matching of Low Solidity Diffuser With High Pressure Ratio Centrifugal Compressor,” 7th International Conference on Pumps and Fans (ICPF 2015), Hangzhou, China, Oct. 18–21.
Tamaki, H. , Nakao, H. , and Saito, M. , 1999, “ The Experimental Study of Matching Between Centrifugal Compressor Impeller and Diffuser,” ASME J. Turbomach., 121(1), pp. 113–118. [CrossRef]
Casey, M. , and Rusch, D. , 2014, “ The Matching of a Vaned Diffuser With a Radial Compressor Impeller and Its Effect on the Stage Performance,” ASME J. Turbomach., 136(12), p. 121004. [CrossRef]
Casey, M. V. , Dalbert, P. , and Shurter, E. , 1990, “ Radial Compressor Stage for Low Flow Coefficients,” 4th European Congress on Fluid Machinery for Oil, Petrochemical and Related Industries, The Hague, The Netherlands, May 21–23, IMechE Paper No. C403/004.
Rusch, D. , and Casey, M. , 2012, “ The Design Space Boundaries for High Flow Capacity Centrifugal Compressors,” ASME Paper No. GT2012-68105.
Dixon, S. L. , and Hall, C. , 2014, Fluid Mechanics and Thermodynamics of Turbomachinery, 7th ed., Butterworth-Heinemann, Oxford, UK, pp. 53–61: 80–83.
Whitfield, A. , and Baines, N. C. , 1990, Design of Radial Turbomachines, Longman Scientific and Technical, Harlow, Essex, UK, pp. 94–99.
Senoo, Y. , Hayami, H. , and Ueki, H. , 1983, “ Low-Solidity Tandem-Cascade Diffusers for Wide-Flow-Range Centrifugal Blowers,” ASME Paper No. 83-GT-3.
Osbone, C. , and Sorokes, J. , 1988, “ The Application of Low Solidity Diffusers in Centrifugal Compressors,” Flow in Non-Rotating Turbomachinery Component, ASME FED, Vol. 69, pp. 89–101.
Sorokes, J. , 1995, “ Industrial Centrifugal Compressors—Design Considerations,” ASME Paper No. 95-WA/PID-2.
Hayami, H. , Research and Development of a Transonic Turbo Compressor, Turbomachinery Fluid Dynamics and Heat Transfer, Marcel Dekker, Inc, New York, pp. 69–77.
Oh, J. S. , and Agrawal, G. L. , 2007, “ Numerical Investigation of Low Solidity Vaned Diffuser Performance in a High-Pressure Centrifugal Compressor Part I: Influence of Vane Solidity,” ASME Paper No. GT2007-27260.
Tamaki, H. , Kawakubo, T. , Unno, M. , Abe, S. , and Majima, K. , 2014, “ Performance Improvement of Multistage Centrifugal Compressor With Low Flow-Rate Stages Based on Factory Acceptance Test Data,” ASME Paper No. GT2014-25156.
Tamaki, H. , and Yamaguchi, S. , 2007, “ The Experimental Study of Matching Between Centrifugal Compressor Impeller and Vaneless Diffusers for Turbochargers,” ASME Paper No. GT2007-28300.
Denton, J. D. , 1993, “ Loss Mechanism in Turbomachines,” ASME J. Turbomach., 115(4), pp. 621–656. [CrossRef]

Figures

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Fig. 1

Ratio of kinetic energy to total energy at impeller outlet

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Fig. 2

Impeller discharge Mach number and peripheral Mach number to achieve pressure ratio of 4:1

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Fig. 3

Tested diffusers [1]: (a) vaned diffuser (VD10) and (b) low solidity diffuser (S7)

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Fig. 4

Compressor performance (VD10, S4, S7, S8, VL) [1]: (a) stage pressure ratio and (b) efficiency

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Fig. 5

Definition of compressor operating range [1]

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Fig. 6

Result of oil flow visualization at Mu = 0.9 (S7 and S4): (a) S7 shroud side, (b) S7 hub side, (c) S4 shroud side, and (d) S4 hub side

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Fig. 7

Change of surge line

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Fig. 8

Pressure recovery factor [1]

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Fig. 9

Effect of Cp6 on compressor performance [1]: (a) stage pressure ratio and (b) stage efficiency at design speed

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Fig. 10

Effect of solidity on pressure recovery factor

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Fig. 11

Schematic of combination of impeller with diffuser with choking in impeller: (a) impeller and diffuser characteristics and (b) nondimensional pressure rises in compressor

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Fig. 12

Schematic of combination of impeller with diffuser with choking in vaned diffuser: (a) impeller and diffuser characteristics and (b) nondimensional pressure rises in compressor

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Fig. 13

Imaginary throat width [1]

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Fig. 14

Compressor performance with VD10, S8, and S8C diffusers [1]: (a) stage pressure ratio and (b) stage efficiency

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Fig. 15

Static pressure and Mach number distribution of vaned diffuser VD10: (a) Mu = 0.90 and (b) Mu = 1.20

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Fig. 16

Static pressure and Mach number distributions of low solidity diffuser S8C: (a) Mu = 0.90 and (b) Mu = 1.20

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Fig. 17

Compressor performance (VD09, S7C, and S7) [1]: (a) stage pressure ratio and (b) stage efficiency

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Fig. 19

Example of characteristics of compressor with vaneless and vaned diffuser: (a) vaneless diffuser and (b) Vaned diffuser

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Fig. 20

Compressor performance (LD1, LD2, LD4, LD5, LD6 and VL): (a) stage pressure ratio, (b) stage efficiency, and (c) work factor of low solidity diffusers at Mu = 1.45 and vaneless diffuser at Mu = 1.16, 1.33, and 1.45

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Fig. 21

Compressor performance (VD1, LD3, and LD4): (a) stage pressure ratio and (b) stage efficiency

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Fig. 22

Compressor performance (LD5, LD51, LD52): (a) stage pressure ratio and (b) stage efficiency

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Fig. 23

Compressor performance (LD6, LD61, and LD62): (a) stage pressure ratio and (b) stage efficiency

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Fig. 24

Compressor-A performance [14]

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Fig. 25

Characteristics of compressor-A: (a) maximum flow coefficient at tested Mu and (b) calculated vaneless diffuser choking flow rate (Mu = 1.12,1.41)

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Fig. 26

Flow coefficient at choke, mild surge and surge at Mu = 1.41 (compressor-A)

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Fig. 27

Compressor-B performance

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Fig. 28

Flow coefficient at choke, peak pressure ratio and surge at Mu = 1.61 (compressor-B)

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Fig. 29

Peripheral Mach number and stage efficiencies: (a) compressor-A and (b) compressor-B

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Fig. 30

Loss generation in vaneless diffuser and volute

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Fig. 31

Comparison between Eq. (35) and Casey and Rusch [3] (R1 = impeller inlet mean radius, R2 = impeller outer radius, n = polytropic exponent).

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Fig. 32

Numbers in subscript and locations in compressor: (a) vaned diffuser and (b) vaneless diffuser

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