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Research Papers

Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry: Part II—Detailed Flow 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

Animations of the unsteady PIV are included in the test case DVD [26].

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

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

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 23, 2014; final manuscript received July 28, 2014; published online September 30, 2014. Editor: Ronald Bunker.

J. Turbomach 137(3), 031004 (Sep 30, 2014) (10 pages) Paper No: TURBO-14-1167; doi: 10.1115/1.4028298 History: Received July 23, 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. In Part I it was shown that an one-sided diffuser clearance is able to contribute to an increase in flow range, stall margin, pressure ratio, and efficiency. In order to reveal the relevant flow phenomena, in Part II the results of detailed measurements of the pressure distribution at diffuser exit and particle image velocimetry (PIV) measurements inside the diffuser channel performed at three clearance configurations and three diffuser angles at a fixed radial gap are discussed. It was found that, for defined diffuser configurations, the clearance flow amplifies the diffuser throat vortex capable to reduce the loading of the highly loaded vane pressure side and to support a more homogenous diffuser flow. It turned out that the co-action of the geometry parameter diffuser vane angle and diffuser clearance height is of particular importance. 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

Measurement planes of probe measurements

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Fig. 2

Implementation of PIV at centrifugal compressor test rig

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Fig. 3

Measurement planes of PIV measurements

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Fig. 4

Investigation area and impeller blade positions

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Fig. 5

Total pressure distribution at diffuser vane exit (7M; r4/r2 = 1.14; α4SS = 4.5 deg; nred/n0 = 0.8; P1)

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Fig. 6

Total pressure distribution at diffuser vane exit (7M; r4/r2 = 1.14; α4SS = 16.5 deg; nred/n0 = 0.8; P1)

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Fig. 7

Total pressure distribution at diffuser vane exit (7M; r4/r2 = 1.14; α4SS = 22.0 deg; nred/n0 = 0.8; P1)

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Fig. 8

Definition of deviation angle in the diffuser passage

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Fig. 9

Unsteady absolute velocity (r4/r2 = 1.14; α4SS = 16.5 deg; s/b = 3%; z/b = 50%; nred/n0 = 0.8; P1; PIV)

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Fig. 10

Unsteady deviation angle (r4/r2 = 1.14; α4SS = 16.5 deg; s/b = 3%; z/b = 50%; nred/n0 = 0.8; P1; PIV)

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Fig. 11

Influence of clearance on diffuser throat vortex

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Fig. 12

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 4.5 deg; s/b = 0%; nred/n0 = 0.8; P1; PIV)

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Fig. 13

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 4.5 deg; s/b = 3%; nred/n0 = 0.8; P1; PIV)

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Fig. 14

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 4.5 deg; s/b = 6%; nred/n0 = 0.8; P1; PIV)

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Fig. 15

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 16.5 deg; s/b = 0%; nred/n0 = 0.8; P1; PIV)

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Fig. 16

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 16.5 deg; s/b = 3%; nred/n0 = 0.8; P1; PIV)

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Fig. 17

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 16.5 deg; s/b = 6%; nred/n0 = 0.8; P1; PIV)

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Fig. 18

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 22.0 deg; s/b = 0%; nred/n0 = 0.8; P1; PIV)

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Fig. 19

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 22.0 deg; s/b = 3%; nred/n0 = 0.8; P1; PIV)

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Fig. 20

Absolute velocity (left) and deviation angle (right) (time averaged; r4/r2 = 1.14; α4SS = 22.0 deg; s/b = 6%; nred/n0 = 0.8; P1; PIV)

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Fig. 21

Deviation angle at diffuser front wall (r4/r2 = 1.14; α4SS = 16.5 deg; s/b = 6%; z/b = 20%; nred/n0 = 0.8; P1; PIV)

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Fig. 22

Deviation angle at diffuser front wall (r4/r2 = 1.14; α4SS = 22.0 deg; s/b = 6%; z/b = 20%; nred/n0 = 0.8; P1; PIV)

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Fig. 23

Absolute velocity at diffuser front wall: correlation between flow angle α4SS and flow path length Δl (r4/r2 = 1.14; s/b = 3%; z/b = 20%; nred/n0 = 0.8; P1; PIV)

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