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Research Papers

An Experimental Study of Loss Sources in a Fan Operating With Continuous Inlet Stagnation Pressure Distortion

[+] Author and Article Information
Ewan J. Gunn

e-mail: ejg55@cam.ac.uk

Yann Colin

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

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received July 17, 2012; final manuscript received September 3, 2012; published online June 24, 2013. Editor: David Wisler.

J. Turbomach 135(5), 051002 (Jun 24, 2013) (10 pages) Paper No: TURBO-12-1151; doi: 10.1115/1.4007835 History: Received July 17, 2012; Revised September 03, 2012

The viability of boundary layer ingesting (BLI) engines for future aircraft propulsion is dependent on the ability to design robust, efficient engine fan systems for operation with continuously distorted inlet flow. A key step in this process is to develop an understanding of the specific mechanisms by which an inlet distortion affects the performance of a fan stage. In this paper, detailed full-annulus experimental measurements of the flow field within a low-speed fan stage operating with a continuous 60 deg inlet stagnation pressure distortion are presented. These results are used to describe the three-dimensional fluid mechanics governing the interaction between the fan and the distortion and to make a quantitative assessment of the impact on loss generation within the fan. A 5.3 percentage point reduction in stage total-to-total efficiency is observed as a result of the inlet distortion. The reduction in performance is shown to be dominated by increased loss generation in the rotor due to off-design incidence values at its leading edge, an effect that occurs throughout the annulus despite the localized nature of the inlet distortion. Increased loss in the stator row is also observed due to flow separations that are shown to be caused by whirl angle distortion at rotor exit. By addressing these losses, it should be possible to achieve improved efficiency in BLI fan systems.

Copyright © 2013 by ASME
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Figures

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Fig. 1

Meridional view of the rig, to scale

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Fig. 2

Comparison of rotor blade sections for the present rig and NASA Rotor 67 [28]. Hub, midspan, and tip are shown in black, red, and blue, respectively.

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Fig. 3

36 deg sector of the measurement grid at station 2

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Fig. 4

Schematic view looking into the rig intake with a 60 deg gauze sector in place

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Fig. 5

Stage total-to-static pressure rise and efficiency characteristics at constant rotor speed

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Fig. 6

Contours of stagnation pressure upstream of the rotor

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Fig. 7

Contours of static pressure upstream of the rotor

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Fig. 8

Contours of absolute whirl angle upstream of the rotor

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Fig. 9

Contours of radial angle upstream of the rotor

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Fig. 10

Contours of axial velocity at rotor inlet and exit

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Fig. 11

Contours of stagnation and static pressure at rotor exit (station 3)

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Fig. 12

Contours of absolute whirl angle and radial angle at rotor exit (station 3)

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Fig. 13

Contours of stagnation pressure at stator exit (station 4) in clean and distorted flow

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Fig. 18

Meridional view of the rotor showing the data used in the kinematic estimate of radial particle displacement

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Fig. 19

Cut along a blade-to-blade stream surface showing the kinematic estimate of circumferential particle displacement

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Fig. 17

Examples of two rotor inlet velocity triangles in distorted flow at 70% span compared with the design condition (shown in gray)

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Fig. 16

Absolute whirl angle, axial velocity and incidence variations at rotor inlet (station 2) in distorted flow. Incidence was defined positive for flow onto the pressure surface.

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Fig. 15

Breakdown of lost work generation in the rotor with DC60 = 0.83 distortion

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Fig. 14

Six tracked sectors overlaid on contours of stagnation pressure at rotor inlet and exit

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