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Research Papers

Improved Diffuser/Volute Combinations for Centrifugal Compressors

[+] Author and Article Information
T. Steglich, J. Kitzinger, J. R. Seume

Institute for Turbomachinery and Fluid Dynamics, Leibniz University Hannover, 30167 Hannover, Germany

R. A. Van den Braembussche, J. Prinsier

 von Karman Institute for Fluid Dynamics, Sint-Genesius-Rode, Belgium

J. Turbomach 130(1), 011014 (Jan 25, 2008) (9 pages) doi:10.1115/1.2749296 History: Received January 11, 2006; Revised January 23, 2007; Published January 25, 2008

Internal volutes have a constant outer radius, slightly larger than the diffuser exit radius, and the circumferential increase of the cross section is accommodated by a decrease of the inner radius. They allow the design of compact radial compressors and hence are very attractive for turbochargers and high-pressure pipeline compressors, where small housing diameters have a favorable impact on weight and cost. Internal volutes, however, have higher losses and lower pressure rise than external ones, in which the center of the cross sections is located at a larger radius than the diffuser exit. This paper focuses on the improvement of the internal volute performance by taking into account the interaction between the diffuser and the volute. Two alternative configurations with enhanced aerodynamic performance are presented. The first one features a novel, nonaxisymmetric diffuser̸internal volute combination. It demonstrates an increased pressure ratio and lower loss over most of the operating range at all rotational speeds compared with a symmetric diffuser̸internal volute combination. The circumferential pressure distortion at off design operation is slightly larger than in the original configuration with a concentric vaneless diffuser. Alternatively, a parallel-walled diffuser with low-solidity vanes and an internal volute allows a reduction of the unsteady load on the impeller and an improved performance, approaching that of a vaneless concentric diffuser with a large external volute.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of the test facility

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Figure 2

Experimental performance map of the original compressor with concentric diffuser and an internal volute indicating the points of low, nominal, and maximum mass flows

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Figure 3

Meridional cross sections at θ=300deg of an internal volute with a conventional concentric diffuser (a) and an asymmetric one with the diffuser wall reduced to 25% (b)

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Figure 4

Schematic of the four compressor configurations (the dark gray area defines the convergent vaneless diffuser wall, and the light gray area defines the parallel LSD wall): (a) internal volute+concentric diffuser (IN), (b) internal volute+asymmetric diffuser (AD), (c) external volute+concentric diffuser (EX), and (d) internal enlarged volute+LS diffuser (LSD)

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Figure 5

Axial view of the asymmetric diffuser with a 25% wall and a stepwise (a) or gradual (b) variation of the diffuser wall in the tongue region

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Figure 6

Calculated static pressure rise and loss coefficients of the internal volute as a function of the remaining fraction of diffuser wall (14,000rpm)

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Figure 7

Static pressure distribution (predicted by CFD, in Pa) at θ=180° in the internal volute with the diffuser wall reduced to 25% (mred=4.573kg∕s, nred=14,000rpm)

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Figure 8

Experimental performance map of the compressor with an asymmetric diffuser

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Figure 9

Circumferential static pressure distribution at impeller outlet (asymmetric diffuser, 14,000rpm)

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Figure 10

Circumferential static pressure distribution at impeller outlet (concentric diffuser, 14,000rpm)

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Figure 11

Calculated static pressure rise and total pressure loss coefficients for different geometries and mass flows

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Figure 12

Total pressure distribution (predicted by CFD in Pa) at midspan of the optimized LSD at 18,000rpm for mred=(a) 4.525, (b) 6.632, and (c) 7.655kg∕s

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Figure 13

Experimental performance map of the compressor with a LSD

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Figure 14

Experimental performance map of the compressor with a concentric diffuser and an external volute

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Figure 15

Circumferential static pressure distributions on the hub wall at the diffuser inlet, midchord, and the trailing edge radius of the LSD (mred=6.9kg∕s, nred=18,000rpm)

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Figure 16

Comparison of pressure ratio and isentropic efficiency for all four configurations at 14,000rpm: (a) internal volute+concentric diffuser (IN), (b) internal volute+asymmetric diffuser (AD), (c) external volute+concentric diffuser (EX), and (d) internal enlarged volute+LS diffuser (LSD)

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Figure 17

Comparison of pressure ratio and isentropic efficiency for all four configurations at 16,500rpm

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Figure 18

Comparison of pressure ratio and isentropic efficiency for all four configurations at 18,000rpm

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