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Research Papers

Performance Improvement of a Centrifugal Compressor Stage by Increasing Degree of Reaction and Optimizing Blade Loading of a 3D Impeller

[+] Author and Article Information
Takanori Shibata, Manabu Yagi

Energy and Environmental Systems Laboratory, Hitachi, Ltd., 7-2-1 Omika-cho, Hitachi-shi, Ibaraki-ken 319-1221, Japan

Hideo Nishida, Hiromi Kobayashi, Masanori Tanaka

Tsuchiura Research Laboratory, Hitachi Plant Technologies, Ltd., 603 Kandatsu-machi, Tsuchiura-shi, Ibaraki-ken 300-0013, Japan

J. Turbomach 133(2), 021004 (Oct 19, 2010) (8 pages) doi:10.1115/1.4000565 History: Received July 17, 2009; Revised July 24, 2009; Published October 19, 2010; Online October 19, 2010

Performance improvement of 3D impellers in a high specific speed range was investigated using computational fluid dynamics analyses and experimental tests. In order to reduce the loss production within the stator passages, the backsweep angle of the impellers was increased. At the same time, the inlet-to-exit relative velocity diffusion ratio was also increased by increasing the impeller exit width to prevent the reduction in the pressure ratio. Moreover, the blade loading distribution at the impeller shroud side was optimized to suppress the surge margin reduction caused by the increased relative velocity diffusion ratio. Five types of unshrouded impellers were designed, manufactured, and tested to evaluate the effects of blade loading, backsweep angle, and relative velocity diffusion ratio on the compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the compressor stage efficiency was increased by 5% compared with the base design without reducing the pressure coefficient and surge margin. It was concluded that an increased relative velocity diffusion ratio coupled with large backsweep angle was a very effective way to improve the compressor stage efficiency. An appropriate blade loading distribution was also important in order to achieve a wide operating range as well as high efficiency.

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References

Figures

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Figure 1

Comparison of single stage loss production between the conventional design and the ideal state

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Figure 2

Effect of a relative velocity diffusion ratio on compressor surge margin

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Figure 3

Analytical results of the effects of W1s/W2 and β2 on compressor performance obtained using the in-house mean-line code PRECENT

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Figure 4

Calculated flow patterns near the surge point for the conventional design impeller

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Figure 5

Blade loading and relative velocity distributions on the shroud side

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Figure 6

Blade loading effects on the impeller characteristic curves obtained using CFD

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Figure 7

Comparison of meridional sections between the developed and conventional impellers

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Figure 8

Blade loading and blade angle distributions on the shroud side

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Figure 9

Compressor test apparatus

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Figure 10

Model compressor test section

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Figure 11

Measured performance characteristics of FL_A (vaned) and BL (ribbed)

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Figure 12

Measured performance characteristics of FL_B (ribbed) and BL (ribbed)

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Figure 13

Test results of the effect of W1s/W2 on compressor performance of FL impellers (ribbed)

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Figure 14

Test results of the effect of W1s/W2 on the operating range of FL and ML impellers (ribbed)

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