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TECHNICAL PAPERS

Engine Design Studies for a Silent Aircraft

[+] Author and Article Information
Cesare A. Hall, Daniel Crichton

Department of Engineering, Whittle Laboratory, Madingley Road, Cambridge, U.K

J. Turbomach 129(3), 479-487 (Jul 23, 2006) (9 pages) doi:10.1115/1.2472398 History: Received July 13, 2006; Revised July 23, 2006

The Silent Aircraft Initiative is a research project funded by the Cambridge-MIT Institute aimed at reducing aircraft noise to the point where it is imperceptible in the urban environments around airports. The propulsion system being developed for this project has a thermodynamic cycle based on an ultrahigh bypass ratio turbofan combined with a variable area exhaust nozzle and an embedded installation. This cycle has been matched to the flight mission and thrust requirements of an all-lifting body airframe, and through precise scheduling of the variable exhaust nozzle, the engine operating conditions have been optimized for maximum thrust at top-of-climb, minimum fuel consumption during cruise, and minimum jet noise at low altitude. This paper proposes engine mechanical arrangements that can meet the cycle requirements and, when installed in an appropriate airframe, will be quiet relative to current turbofans. To reduce the engine weight, a system with a gearbox, or some other form of shaft speed reduction device, is proposed. This is combined with a low-speed fan and a turbine with high gap-chord spacing to further reduce turbomachinery source noise. An engine configuration with three fans driven by a single core is also presented, and this is expected to have further weight, fuel burn, and noise benefits.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Noise levels for a current 250 passenger aircraft compared with the Silent Aircraft target

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Figure 2

A 3-D rendering of a candidate Silent Aircraft airframe and propulsion system, taken from (11)

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Figure 3

View of the surface mesh for a four-engine installation, taken from (17)

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Figure 4

Contours of Mach number through a four-engine installation, taken from (17)

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Figure 5

Schematic of engine layout showing station numbering, adapted from (18)

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Figure 6

Evolution of the Silent Aircraft engine cycle at top-of-climb assuming a four-engine system

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Figure 7

Operation of the Silent Aircraft engine fan for a variable nozzle design

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Figure 8

Operation of the Silent Aircraft engine fan for a fixed nozzle design

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Figure 9

Variation in fan efficiency, jet noise, and fan tip relative Mach number with nozzle area.

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Figure 10

Design A: 3-spool conventional turbofan design for the Silent Aircraft

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Figure 11

Design B: Geared turbofan for the Silent Aircraft with axial-radial HP compressor

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Figure 12

Design C: Geared turbofan for the Silent Aircraft modified for lower noise

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Figure 13

Design D: Multiple fan version of a geared turbofan for the Silent Aircraft

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Figure 14

Variation in rearward fan noise with design fan pressure ratio based on ESDU 98008 (22)

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Figure 15

Variation in cruise fuel burn with design fan pressure ratio and installation configuration

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