Investigation of Unsteady Flow Field in a Vaned Diffuser of a Transonic Centrifugal Compressor

[+] Author and Article Information
Seiichi Ibaraki, Tetsuya Matsuo, Takao Yokoyama

 Nagasaki Research and Development Center, Mitsubishi Heavy Industries, Ltd., 1-1 Akunoura-machi, Nagasaki 850-8610, Japan

J. Turbomach 129(4), 686-693 (Aug 11, 2006) (8 pages) doi:10.1115/1.2720505 History: Received July 23, 2006; Revised August 11, 2006

Transonic centrifugal compressors are used with high-load turbochargers and turboshaft engines. These compressors usually have a vaned diffuser to increase the efficiency and the pressure ratio. To improve the performance of such a centrifugal compressor, it is required to optimize not only the impeller but also the diffuser. However the flow field of the diffuser is quite complex and unsteady because of the impeller located upstream. Although some research on vaned diffusers has been published, the diffuser flow is strongly dependent on the particular impeller exit flow, and some of the flow physics remain to be elucidated. In the research reported here, detailed flow measurements within a vaned diffuser were conducted using a particle image velocimetery (PIV). The vaned diffuser was designed with high subsonic inlet conditions marked by an inlet Mach number of 0.95 for the transonic compressor. As a result, a complex three-dimensional flow with distortion between the shroud and the hub was observed. Also, unsteady flow accompanying the inflow of the impeller wake was confirmed. Steady computational flow analysis was performed and compared with the experimental results.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Test impeller and diffuser

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Figure 2

Cross section and measurement locations

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Figure 3

Compressor stage characteristics

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Figure 4

Test section of diffuser

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Figure 5

PIV measurement setup

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Figure 6

Absolute velocity distribution and velocity vectors

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Figure 7

Flow angle distribution and velocity vectors

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Figure 8

Comparison of flow angle distribution and velocity vectors at peak efficiency point

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Figure 9

Comparison of pitchwise averaged flow angle and meridional velocity

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Figure 10

Unsteady flow angle distribution and velocity vectors measured by PIV

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Figure 11

Time-wise changes of flow angle in the vaned diffuser

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Figure 12

Computational mesh

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Figure 13

Vortex core colored with vorticity and normalized helicity

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Figure 14

Limiting streamline on vane and hub surface

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Figure 15

Total pressure distribution

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Figure 16

Entropy distribution




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