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Research Papers

Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry—Part I: Compressor Performance Analysis

[+] Author and Article Information
Stefan Ubben

Institute of Jet Propulsion and Turbomachinery,
RWTH Aachen University,
Aachen 52062, Germany
e-mail: stefan.ubben@man.eu

Reinhard Niehuis

Institute of Jet Propulsion and Turbomachinery,
RWTH Aachen University,
Aachen 52062, Germany
e-mail: reinhard.niehuis@unibw.de

1Present address: MAN Diesel & Turbo SE, Steinbrinkstraße 1, Oberhausen 46145, Germany.

2Present address: Institute of Jet Propulsion, Universitaet der Bundeswehr Munich, Neubiberg 85577, Germany.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 22, 2014; final manuscript received July 28, 2014; published online September 30, 2014. Editor: Ronald Bunker.

J. Turbomach 137(3), 031003 (Sep 30, 2014) (10 pages) Paper No: TURBO-14-1165; doi: 10.1115/1.4028297 History: Received July 22, 2014; Revised July 28, 2014

Adjustable diffuser vanes offer an attractive design option for centrifugal compressors applied in industrial applications. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall is still not satisfying. This two-part paper summarizes results of experimental investigations performed with an industrial-like centrifugal compressor. Particular attention was directed toward the influence of the diffuser clearance on the operating behavior of the entire stage, the pressure recovery in the diffuser, and on the diffuser flow by a systematic variation of the parameters diffuser clearance height, diffuser vane angle, radial gap between impeller exit and diffuser inlet, and rotor speed. Compressor map measurements provide a summary of the operating behavior related to diffuser geometry and impeller speed, whereas detailed flow measurements with temperature and pressure probes allow a breakdown of the losses between impeller and diffuser and contribute to a better understanding of relevant flow phenomena. The results presented in Part I show that an one-sided diffuser clearance does not necessarily has a negative impact on the operation and loss behavior of the centrifugal compressor, but instead may contribute to an increased pressure ratio and improved efficiency as long as the diffuser passage is broad enough with respect to the clearance height. The flow phenomena responsible for this detected performance behavior are exposed in Part II, where the results of detailed measurements with pressure probes at diffuser exit and particle image velocimetry (PIV) measurements conducted inside the diffuser channel are discussed. The experimental results are published as an open computational fluid dynamics (CFD) testcase “Radiver 2.”

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References

Figures

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Fig. 1

Centrifugal compressor test bed

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Fig. 2

Cross section of the compressor stage

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Fig. 3

Compressor stage with dismounted front wall

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Fig. 4

Variable and constant diffuser parameters

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Fig. 5

Diffuser vane with one-sided clearance

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Fig. 6

Probe measurement technique

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Fig. 7

Investigated diffuser configurations

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Fig. 8

Characteristic lines for r4/r2 = 1.10

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Fig. 9

Characteristic lines for r4/r2 = 1.14

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Fig. 10

Influence of diffuser vane angle and clearance on relative flow range

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Fig. 11

Influence of diffuser vane angle and clearance on choke flow rate

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Fig. 12

Influence of diffuser vane angle and clearance on change in total pressure ratio

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Fig. 13

Influence of diffuser vane angle and clearance on change in isentropic efficiency

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Fig. 14

Influence of diffuser vane angle and clearance on maximum efficiency

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Fig. 15

Operating points of steady probe measurements (r4/r2 = 1.14; nred/n0 = 0.8; P1)

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Fig. 16

Total temperature at diffuser exit (8M; r4/r2 = 1.14; nred/n0 = 0.8; P1)

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Fig. 17

Averaged total pressures and Mach numbers in measurement planes 2M, 7M, 8M and E (r4/r2 = 1.14; nred/n0 = 0.8; P1)

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Fig. 18

Pressure recovery (cp) and total pressure loss (ω) of (diffuser 1), (diffuser), (diffuser+collector) (r4/r2 = 1.14; α4SS = 16.5 deg; nred/n0 = 0.8; P1)

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Fig. 19

Isentropic efficiencies (total/total) of (impeller), (impeller+diffuser 1), (impeller+diffuser), (impeller+diffuser+collector) (r4/r2 = 1.14; α4SS = 16.5 deg; nred/n0 = 0.8; P1)

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