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Research Papers

Investigation of Pre-Stall Behavior in an Axial Compressor Rotor—Part II: Flow Mechanism of Spike Emergence

[+] Author and Article Information
Yanhui Wu1

School of Power and Energy,  Northwestern Polytechnical University, Xi’an, Shanxi 710072, People’s Republic of Chinawyh@nwpu.edu.cn

Qingpeng Li, Jiangtao Tian, Wuli Chu

School of Power and Energy,  Northwestern Polytechnical University, Xi’an, Shanxi 710072, People’s Republic of China

1

Corresponding author.

J. Turbomach 134(5), 051028 (Jun 05, 2012) (10 pages) doi:10.1115/1.4004753 History: Received June 21, 2011; Revised July 24, 2011; Published June 05, 2012

To investigate the pre-stall behavior of an axial flow compressor rotor, which was experimentally observed with spike-type stall inception, systematic experimental and whole-passage simulations were laid out to analyze the internal flow fields in the test rotor. In this part, emphases were put on the analyses of the flow fields of whole-passage simulation, which finally diverged, and the objective was to uncover the flow mechanism of short length scale disturbance (or spike) emergence. The numerical result demonstrated that the test rotor was of spike-type stall initiation. The numerical probes, arranged ahead of the rotor to monitor the static pressure variation, showed that there first appear two pips on the curves. After one rotor revolution, there was only one pip left, spreading at about 33.3% rotor speed. This propagation speed was almost the same as that of the spike observed in experiments. The further analysis of the flow field revealed a concentrated blockage sector on the flow annuls ahead of rotor developed gradually with the self-adjustment of flow fields. The two pins on monitoring curves corresponded to two local blockage regions in near-tip passages, and were designated as B1 and B2, respectively. The correlation between the tip secondary vortices (TSVs) in the preceding and native passages was the flow mechanism for propagation of B2 and B1, thereby leading to their spread speed approximate to the active period of the TSV in one passage. Furthermore, the self-sustained unsteady cycle of TSVs was the underlying flow mechanism for the occurrence of the so-called “tip clearance spillage flow” and “tip clearance backflow.” Because B2 was the tip-front of the blockage sector, TSVs associated with its propagation became stronger and stronger, so that the “tip clearance backflow” induced by it was capable of spilling into the next passage below the blade tip. This phenomenon was regarded as the threshold event where B2 started to evolve into a spike. The distinctive flow feature during the development stage of the spike was the occurrence of a separation focus on the suction side in the affected passages, which changed the self-sustained unsteady cycle of the TSV substantially. A three-dimensional vortex originating from this focus led to a drastic increase in the strength of the TSV, which, in turn, led to a rapid increase in the “tip clearance backflow” induced by the TSV and the radial extent of spillage flow.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Cross-sectional diagram of the test rig

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Figure 2

Typical stalling pattern of the test rotor

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Figure 3

Blade passage and grid topology

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Figure 4

The comparison between the computed and experimental pressure rise characteristics

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Figure 5

Time histories of inlet/outlet mass flow rate

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Figure 6

Static pressure traces at the location of the ten numerical probes

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Figure 7

Static Distributions on the plane 100% tip axial chord ahead of rotor and entropy distributions on a surface of revolution at blade tip

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Figure 8

The detailed flow structure near tip from t = 1550 to t = 1600. Middle: distribution of negative axial velocity at blade tip section; upper left corner: locally zoomed leakage streamlines; lower right corner: locally zoomed casing static pressure distributions.

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Figure 9

Limiting streamlines on the suction side and pressure side of Blade 17

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Figure 10

Pressure distributions on six axial cuts at instants just before the occurrence of “tip clearance backflow” during t = 1550–1800 associated with propagation of B2

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Figure 11

Illustration of “tip clearance backflow” forming “tip clearance spillage flow” at t = 1910

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Figure 12

Limiting streamlines on the blade suction sides at t = 1835, 2110, 2230, 2350, 2470, and 2590

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Figure 13

Vortical structures in the affected passage at instants t = 2350 and 2590

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Figure 14

The “tip clearance backflow” occurring at instants t = 1850, 2370, and 2570

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Figure 15

Entropy distributions on the flow annulus ahead of rotor at 16% tip axial chord at t = 1850, 2370, and 2570

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