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Research Papers: Gas Turbines: Aircraft Engine

Full-Scale Turbofan Demonstration of a Deployable Engine Air-Brake for Drag Management Applications1

[+] Author and Article Information
Parthiv N. Shah

ATA Engineering, Inc.,
San Diego, CA 92128
e-mail: parthiv.shah@ata-e.com

Gordon Pfeiffer

ATA Engineering, Inc.,
San Diego, CA 92128
e-mail: gordon.pfeiffer@ata-e.com

Rory Davis

ATA Engineering, Inc.,
San Diego, CA 92128
e-mail: rory.davis@ata-e.com

Thomas Hartley

Williams International,
Walled Lake, MI 48390
e-mail: THartley@williams-int.com

Zoltán Spakovszky

Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: zolti@mit.edu

Contributed by the Aircraft Engine Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 9, 2017; final manuscript received June 5, 2017; published online August 1, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(11), 111202 (Aug 01, 2017) (13 pages) Paper No: GTP-17-1053; doi: 10.1115/1.4037155 History: Received February 09, 2017; Revised June 05, 2017

This paper presents the design and full-scale ground-test demonstration of an engine air-brake (EAB) nozzle that uses a deployable swirl vane mechanism to switch the operation of a turbofan's exhaust stream from thrust generation to drag generation during the approach and/or descent phase of flight. The EAB generates a swirling outflow from the turbofan exhaust nozzle, allowing an aircraft to generate equivalent drag in the form of thrust reduction at a fixed fan rotor speed. The drag generated by the swirling exhaust flow is sustained by the strong radial pressure gradient created by the EAB swirl vanes. Such drag-on-demand is an enabler to operational benefits such as slower, steeper, and/or aeroacoustically cleaner flight on approach, addressing the aviation community's need for active and passive control of aeroacoustic noise sources and access to confined airports. Using NASA's technology readiness level (TRL) definitions, the EAB technology has been matured to a level of six, i.e., a fully functional prototype. The TRL-maturation effort involved design, fabrication, assembly, and ground-testing of the EAB's deployable mechanism on a full-scale, mixed-exhaust, medium-bypass-ratio business jet engine (Williams International FJ44-4A) operating at the upper end of typical approach throttle settings. The final prototype design satisfied a set of critical technology demonstration requirements that included (1) aerodynamic equivalent drag production equal to 15% of nominal thrust in a high-powered approach throttle setting (called dirty approach), (2) excess nozzle flow capacity and fuel burn reduction in the fully deployed configuration, (3) acceptable engine operability during dynamic deployment and stowing, (4) deployment time of 3–5 s, (5) stowing time under 0.5 s, and (6) packaging of the mechanism within a notional engine cowl. For a typical twin-jet aircraft application, a constant-speed, steep approach analysis suggests that the EAB drag could be used without additional external airframe drag to increase the conventional glideslope from 3 deg to 4.3 deg, with about 3 dB noise reduction at a fixed observer location.

Copyright © 2017 by ASME
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Figures

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Fig. 1

Technology development roadmap in context of NASA TRL definitions

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Fig. 2

EAB CAD model in two configurations. Translucent green region shows allowable zone boundary. Vane area cutout feature controls effective exit area: (a) stowed and (b) fully deployed (100 deg).

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Fig. 3

Key components of the EAB assembly

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Fig. 4

Photographs of the assembled EAB nozzle: trimetric view (left) and aft-looking-forward view (right)

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Fig. 5

Zoomed-in view of typical CFD domain for arbitrary vane count used a mixing-plane interface

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Fig. 6

Conceptual depiction of engine fan operating point for EAB in different configurations

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Fig. 7

Mixing-plane CFD results for final design in fully deployed (100 deg) configuration: (a) circumferential (swirl)-to-freestream velocity ratio, selected downstream exhaust planes and (b) streamlines colored by swirl angle

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Fig. 8

Two EAB nozzle configurations on FJ44-4 engine: (a) EAB fully deployed and (b) EAB stowed

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Fig. 9

View of engine on OTF2 test stand with far-field microphone on white ground plates arranged in a polar arc array (90–162 deg). Anemometry station in foreground.

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Fig. 10

ΔFg/Fg versus fractional flow capacity for EAB at various deployment angles

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Fig. 11

Measured net thrust reduction (ΔFn/Fg) from stowed (0 deg) to fully deployed (100 deg)

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Fig. 12

Measured fractional flow change (rematched) from stowed (0 deg) to fully deployed (100 deg)

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Fig. 13

Percent gross thrust change versus percent fan speed (N1) EAB at various deployment angles

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Fig. 14

Percent fuel flow change versus percent fan speed (N1) EAB at various deployment angles

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Fig. 15

Percent corrected N2 speed (N2C) versus percent fan speed (N1) EAB at various deployment angles

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Fig. 16

Transient data during deployment

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Fig. 17

Frame-by-frame video analysis of deployment, showing 3–5 s duration

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Fig. 18

Transient data during stowing

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Fig. 19

Frame-by-frame video analysis of stowing, showing < 0.5 s duration

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Fig. 20

Narrowband (4 Hz) SPL spectra at polar angle θ = 90 deg

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Fig. 21

Narrowband (4 Hz) SPL spectra at polar angle θ = 130 deg. Ordinate values arbitrarily shifted relative to previous figure to conceal absolute levels.

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Fig. 22

OASPL deltas relative to referee nozzle at dirty approach power condition at six polar angles. Negative ordinate values indicate noise reduction.

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