Research Papers

Casing Treatment and Inlet Swirl of Centrifugal Compressors

[+] Author and Article Information
Hua Chen

Honeywell Turbo Technologies,
Cheadle Hulme,
Cheshire, SK8 6QS, UK
e-mail: hua.chen@honeywell.com

Vai-Man Lei

Honeywell Turbo Technologies,
Torrance, CA 90505
e-mail: vaiman.lei@honeywell.com

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 1, 2012; final manuscript received September 3, 2012; published online June 5, 2013. Assoc. Editor: David Wisler.

J. Turbomach 135(4), 041010 (Jun 05, 2013) (8 pages) Paper No: TURBO-12-1109; doi: 10.1115/1.4007739 History: Received July 01, 2012; Revised September 03, 2012

Ported shroud is a cost-effective casing treatment that can greatly improve stability of centrifugal compressors. It is widely used in turbochargers and other applications where compressors with a wide flow range are required. This paper reviews the development of the ported shroud concept from its first conception in the 1980 s to its current various configurations and explores the underline mechanisms that deliver the performance improvement. It is explained that, by removing stagnant fluid from impeller inducer shroud end wall boundary-layer region and recirculating it to the impeller inlet, blade loading near the inducer shroud is increased with improved inlet suction. For transonic flow, the ported shroud weakens the shock wave and reduces flow separation on the inducer suction surface. It is argued that the effectiveness of ported shroud is a balance of blade loading and the flow loss inside the ported shroud cavity. The loss needs to be minimized if ported shroud is to be more effective. Blade loading may be increased by various methods, such as using high inducer blade turning and using full-bladed impellers. The blade loading can also be improved by removing flow swirl in ported shroud flow by vanes or imposing negative swirl by vanes in ported shroud. Circumferential flow variation caused by volute housing can be taken into account by variable pitch vanes or by variable port position.

Copyright © 2013 by ASME
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Fig. 1

Ported shroud compressor

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Fig. 2

Effects of ported shroud on a small turbocharger centrifugal compressor (see online publication for color representation)

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Fig. 3

Ribless ported shroud compressor housing [4]

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Fig. 4

Effects of ported shroud length, from Ref. [5]

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Fig. 5

Vaned ported shroud; vane orientation is the same as swirl direction of port flow [6]

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Fig. 6

Effects of keeping swirl of port flow [6] (see online publication for color representation)

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Fig. 7

Counter swirl ported shroud (CSCT) and no swirl casing treatment (NSCT) [7]

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Fig. 8

Effect of counter swirl ported shroud [7]. WOCT: without casing treatment; CT: conventional casing treatment.

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Fig. 9

Effect of ported shroud on flow. Near surge (left), near choke (right). Flow vector (top) and contour (bottom) of circumferentially averaged streamwise velocity are shown.

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Fig. 10

Weaker inducer shockwave due to ported shroud: without ported shroud (left), with ported shroud (right). CFD results from Ref. [8].

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Fig. 11

Meridional flows inside a ported shroud compressor

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Fig. 12

Minimizing loss in ported shroud using vane diffuser [9]

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Fig. 13

Performance improvement by minimizing port flow loss [9] (see online publication for color representation)

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Fig. 14

PIV measurement of flow at inlet region of a ported shroud compressor working near surge

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Fig. 15

Asymmetric ported shrouds from Ref. [13]. Sr is the axial distance between impeller LE and port front. A, B, and C are conventional ported shrouds with different constant Sr values; D to G are asymmetric ported shrouds with Sr as function of azimuth angle.

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Fig. 16

Effects of asymmetric port location on compressor surge flow, from Ref. [13]. See Fig. 15 for additional information. C and G are the best symmetric and asymmetric port locations, respectively.

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Fig. 17

CFD results of flow field inside a constant pitch, vaned ported shroud, showing asymmetric feature

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Fig. 18

Variable pitch vanes in ported shroud. White line indicates tongue position; reduced pitch under the tongue and 180 deg from the tongue.

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Fig. 19

CFD results showing effects of variable pitch; conventional ported shroud with 4 ribs also included




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