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Research Papers

Stall Inception in Low-Pressure Ratio Fans

[+] Author and Article Information
S. Kim, R. P. Grewe

Whittle Laboratory,
University of Cambridge,
1 JJ Thomson Avenue,
Cambridge CB3 0DY, UK

G. Pullan

Whittle Laboratory,
University of Cambridge,
1 JJ Thomson Avenue,
Cambridge CB3 0DY, UK
e-mail: gp10006@cam.ac.uk

C. A. Hall

Whittle Laboratory,
University of Cambridge,
1 JJ Thomson Avenue,
Cambridge CB3 0DY, UK

M. J. Wilson

Rolls-Royce plc, Moor Lane,
Derby, DE21 8BJ, UK

E. Gunn

Turbostream Ltd,
3 Charles Babbage Road,
Cambridge, CB3 0GT, UK

1Present address: R&D Center, Hanwha Aerospace, Republic of Korea.

2Corresponding author.

3Present address: Siemens, Mülheim an der Ruhr, Germany.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received January 14, 2019; final manuscript received January 26, 2019; published online February 22, 2019. Assoc. Editor: Kenneth Hall.

J. Turbomach 141(7), 071005 (Feb 22, 2019) (9 pages) Paper No: TURBO-19-1010; doi: 10.1115/1.4042731 History: Received January 14, 2019; Revised January 26, 2019; Accepted January 28, 2019

A combined experimental and computational test program, with two low-pressure ratio aero-engine fans, has been used to identify the flow mechanisms at stall inception and the subsequent stall cell growth. The two fans have the same rotor tip clearance, annulus design, and downstream stators, but different levels of tip loading. The measurement data show that both the fans stall via spike-type inception, but that the growth of the stall cell and the final cell size is different in each fan. The computations, reproducing both the qualitative and quantitative behavior of the steady-state and transient measurements, are used to identify the flow mechanisms at the origin of stall inception. In one fan, spillage of tip leakage flow upstream of the leading edge plane is responsible. In the other, sudden growth of casing corner separation blockage leads to stall. These two mechanisms are in accord with the findings from core compressors. However, the transonic aerodynamics and the low hub-to-tip radius ratio of the fans lead to the following two findings: first, the casing corner separation is driven by shock-boundary layer interaction and second, the spanwise loading distribution of the fan determines whether the spike develops into full-span or part-span stall and both types of behavior are represented in the present work. Finally, the axial momentum flux of the tip clearance flow is shown to be a useful indicator of the leakage jet spillage mechanism. A simple model is provided that links the tip loading, stagger, and solidity with the tip clearance axial momentum flux, thereby allowing the aerodynamicist to connect, qualitatively, design parameters with the stall behavior of the fan.

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References

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Hewkin-Smith, M., Pullan, G., Grimshaw, S., Greitzer, E., and Spakovszky, Z., 2017, “The Role of Tip Leakage Flow in Spike-Type Rotating Stall Inception,” ASME IGTI Turbo Expo, GT2017-63655, Charlotte, NC.
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Figures

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Fig. 1

The fan test facility at AneCom AeroTest, Germany. (a) AneCom AeroTest noise test facility and (b) the Vital fan.

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Fig. 2

Computational domain for fan simulations

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Fig. 3

Performance characteristics for Vital, 100% speed

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Fig. 4

Spanwise profiles for Vital at the inlet to the bypass duct at peak efficiency and low flow rates

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Fig. 5

Suction-surface limiting streamlines, Vital. (a) Peak efficiency and (b) near stall.

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Fig. 6

Performance characteristics for Fan A, 100% speed

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Fig. 7

Spanwise profiles for Fan A at the inlet to the bypass duct at peak efficiency and low flow rates

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Fig. 8

Measured and computed casing pressure traces at stall-inception for Vital. (a) Experiment and (b) computation.

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Fig. 9

Measured and computed casing pressure traces at stall-inception for Fan A. (a) Experiment and (b) computation.

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Fig. 10

Computed fan outlet entropy during fully developed rotating stall. (a) Vital and (b) Fan A.

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Fig. 11

Computed pressure ratio characteristics (one point per rev) during the stall inception computations of Figs. 8 and 9. (a) Vital and (b) Fan A

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Fig. 12

Computed radial vorticity ωr~ and static pressure Δp~ at 99.5% span during the stall of Vital. (a) t = 1 rev—stable operation, (b) t = 4 revs—stall inception, and (c) t = 4 revs—fully developed stall cell.

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Fig. 13

Iso-surface of the vortex detection “Q” criterion, and instantaneous streamlines, during stall of Vital. (a) t = 1 and (b) t = 4 revs.

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Fig. 14

Computed radial vorticity ωr~ and static pressure Δp~ at 99.5% span during the stall of Fan A. (a) t = 1 rev—stable operation, (b) t = 4 revs—stall inception, and (c) t = 6.5 revs—fully developed stall cell.

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Fig. 15

Iso-surface of the vortex detection “Q” criterion, and instantaneous streamlines, during stall of Fan A. (a) t = 1 and (b) t = 4 revs.

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Fig. 16

Computed pressure distribution at 99.5% span at t = 0 revs in Figs. 8 and 9, Cp=p−p1/(12ρW12)

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Fig. 17

Normalized tip leakage axial momentum flux, μ

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Fig. 18

Schematic of the tip leakage jet of Vital and Fan A, showing the reduced stagger and solidity of Fan A. (a) Vital and (b) Fan A.

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Fig. 19

Performance characteristics for Vital, 100% speed, with the original and modified Spalart–Allmaras model

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Fig. 20

Vital suction-surface streamlines at peak efficiency, with the original and modified Spalart–Allmaras model. (a) Modified SA model and (b) original SA model.

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