Preliminary Fan Design for a Silent Aircraft

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

 Whittle Laboratory, Department of Engineering, Madingley Road, Cambridge, CB3 0DY, United Kingdom

J. Turbomach 129(1), 184-191 (Feb 01, 2006) (8 pages) doi:10.1115/1.2372779 History: Received October 01, 2005; Revised February 01, 2006

Preliminary fan design for a functionally silent aircraft has been performed with noise reduction as the primary goal. For such an aircraft the fan design must, in addition to delivering low cruise fuel burn, enable low jet and fan source noise during takeoff. This requires the fan to be operating at low pressure ratio and high efficiency during takeoff and, for conditions where the relative tip Mach number onto the fan is supersonic, ensuring the primary shock structure is ingested into the blade passage. To meet these requirements, flyover and cruise flow coefficients are matched using a variable area nozzle at the same time as delivering low takeoff FPR. This places the sideline operating point near the shoulder of the characteristic and fixes the top of climb and cruise fan pressure ratios. For a 4-engine, 250pax, 4000nm silent aircraft this approach leads to a top of climb FPR of 1.45, requiring a 39% increase in nozzle area at takeoff. A fan rotor has been designed for this cycle with 20 blades, low tip loading during takeoff, and a 350ms top of climb tip speed.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Reduction in thrust corrected aircraft noise level over time

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Figure 2

Takeoff profile optimization for jet noise outside airport boundary (10000ft runway, airport boundary 450m at the sideline and 1000m from the end of the runway at flyover, sea level ISA+12K conditions)

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Figure 3

Reduction in the required jet area achieved through optimization of the takeoff profile for different peak jet noise requirements

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Figure 4

FPR for a fixed nozzle engine at key operating points for a 250pax, 4000nm aircraft. Four-engine embedded variant=solid black lines, two-engine podded variant=dashed grey lines. (This distinction between the two aircraft variants is followed in the remaining plots.)

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Figure 5

Required nozzle variation to meet both top of climb FPR and takeoff jet noise requirements for two aircraft variants

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Figure 6

Top of climb FPR uniquely defined by specifying flyover FPR, fan capacity, and matching flow coefficient at flyover and cruise

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Figure 7

Required top of climb FPR and nozzle opening at takeoff relative to top of climb to match φ at flyover and cruise conditions for two aircraft variants

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Figure 8

Required top of climb fan blade speed to meet Mrel@tip=1 at specified conditions for two aircraft variants

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Figure 9

Fan characteristic showing lines of fan speed relative to the design point and contours of rotor only polytropic efficiency

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Figure 10

Radial variations in fan pressure ratio and inlet flow coefficient for key operating conditions

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Figure 11

Contours of the relative Mach number at 95% and 75% span when operating at the sideline position

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Figure 12

Swirl and absolute Mach number onto OGVs at key operating points



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