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The Impact of Subsonic Twin Jets on Airport Noise
Subsonic and supersonic aircraft concepts proposed through NASA’s Fundamental Aeronautics Program have multiple engines mounted near one another. Engine configurations with multiple jets introduce an asymmetry to the azimuthal directivity of the jet noise. Current system noise predictions add the jet noise from each jet incoherently, therefore, twin jets are estimated by adding 3 EPNdB to the far-field noise radiated from a single jet. Twin jet effects have the ability to increase or decrease the radiated noise to different azimuthal observation locations. Experiments have shown that twin jet effects are reduced with forward flight and increasing spacings. The current experiment investigates the impact of spacing, and flight effects on airport noise for twin jets. Estimating the jet noise radiated from twin jets as that of a single jet plus 3 EPNdB may be sufficient for horizontal twin jets with an s/d of 4.4 and 5.5, where s is the center-to-center spacing and d is the jet diameter. However, up to a 3 EPNdB error could be present for jet spacings with an s/d of 2.6 and 3.2.
https://ntrs.nasa.gov/search.jsp?R=20120014209 2018-08-06T06:44:11+00:00Z
National Aeronautics and Space Administration
www.nasa.gov
Funded by the Subsonic Fixed Wing and Supersonics
Projects of NASA’s Fundamental Aeronautics Program
The Impact of Subsonic Twin Jets
on Airport Noise
Rick Bozak
NASA Glenn Research Center
18th AIAA/CEAS Aeroacoustics Conference
June 4-6, 2012 Colorado Springs, Colorado
1
National Aeronautics and Space Administration
www.nasa.gov
Outline
• Motivation
• Experiment Setup
• 1/3 Octave SPL Contours
– Effect of jet spacing
– Effect of forward flight
• Effective Perceived Noise Level (EPNL) Calculations
• Conclusion
2
National Aeronautics and Space Administration
www.nasa.gov
Fundamental Aeronautics Program
Subsonic Fixed Wing Project N+3 NRA Concept Vehicles
Boeing MIT Northrop Grumman
Supersonics Project Concept Vehicles
N+3, Boeing N+3, Lockheed Martin N+2, Lockheed Martin
3
National Aeronautics and Space Administration
www.nasa.gov
Configurations
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S-Duct Y-Duct
Nozzles
Single Jet
Bypass Duct
National Aeronautics and Space Administration
www.nasa.gov
Configurations and Conditions
Spacings
s/d
2.63
3.25
4.39
5.54
Azimuthal Angles
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
Jet Conditions
NPR= Nozzle Pressure Ratio
NTR= Nozzle Temperature Ratio
Mfj= Free Jet Mach Number
National Aeronautics and Space Administration
www.nasa.gov
Sound Pressure Levels
• 2-inch conic convergent nozzles
• Actuator and diffraction corrections were made
• Background noise was removed
• Free jet shear layer refraction was corrected for
• Data are presented in 1 foot lossless 1/3 octave sound pressure levels
ΔSPL = SPLtwin – SPLsingle+3dB
6
National Aeronautics and Space Administration
www.nasa.gov
Single Jet + 3dB Contour
7
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
www.nasa.gov
In-plane Measurements – Effect of Spacing
8
s/d
2.63
3.25
4.39
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
www.nasa.gov
In-plane Measurements – Effect of Spacing
9
s/d
2.63
3.25
4.39
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
www.nasa.gov
In-plane Measurements – Effect of Spacing
10
s/d
2.63
3.25
4.39
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
www.nasa.gov
In-plane Measurements – Effect of Forward Flight
11
s/d
2.63
3.25
4.39
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
www.nasa.gov
In-plane Measurements – Effect of Forward Flight
12
s/d
2.63
3.25
4.39
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
www.nasa.gov
In-plane Measurements – Effect of Forward Flight
13
s/d
2.63
3.25
4.39
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
www.nasa.gov
Out-of-plane Measurements – Effect of Spacing
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s/d
2.63
3.25
4.39
5.54
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
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s/d
2.63
3.25
4.39
5.54
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
Out-of-plane Measurements – Effect of Spacing
National Aeronautics and Space Administration
www.nasa.gov 16
s/d
2.63
3.25
4.39
5.54
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
Out-of-plane Measurements – Effect of Spacing
National Aeronautics and Space Administration
www.nasa.gov 17
s/d
2.63
3.25
4.39
5.54
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
Out-of-plane Measurements – Effect of Spacing
National Aeronautics and Space Administration
www.nasa.gov 18
s/d
2.63
3.25
4.39
5.54
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
Out-of-plane Measurements – Effect Forward Flight
National Aeronautics and Space Administration
www.nasa.gov 19
s/d
2.63
3.25
4.39
5.54
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
Out-of-plane Measurements – Effect Forward Flight
National Aeronautics and Space Administration
www.nasa.gov 20
s/d
2.63
3.25
4.39
5.54
NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
Out-of-plane Measurements – Effect Forward Flight
National Aeronautics and Space Administration
www.nasa.gov
Twin Jet Sizing
Nozzle Diameter
Nozz
le S
pac
ing
Military
Supersonics
Subsonic Fixed Wing
Subsonic Fixed Wing
National Aeronautics and Space Administration
www.nasa.gov
Twin Jet Sizing
Nozzle Diameter, inches
Nozz
le S
pac
ing, s/
d
Military
Subsonic Fixed Wing
Supersonics
2.63
3.25
5.54
4.39
Subsonic Fixed Wing
20” 40” 60” 100”
National Aeronautics and Space Administration
www.nasa.gov
EPNL Calculations
• 1 foot lossless data were propagated at standard day
to a 1775 foot linear array (approximate lateral
microphone distance)
• Constant velocity (M=0.3), constant height flyover
• Full-scale nozzle diameters of 20”, 40”, 60” and 100”
• Repeatability of ±0.3 EPNdB
– 95% confidence interval on a single condition and
configuration that was repeated 3 times
EPNL = PNLmax + Duration Factor + Tone Correction Factor
ΔEPNL = EPNLtwin – EPNLsingle+3EPNdB
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National Aeronautics and Space Administration
www.nasa.gov
Twin Jet EPNL Corrections
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NPR NTR Mfj
1.70 3.11 0.00
1.70 3.11 0.10
1.87 3.12 0.30
National Aeronautics and Space Administration
www.nasa.gov
Conclusions
• Coherent interactions between the jets can increase
the peak out-of-plane jet noise 3 dB over a single jet
plus 3dB, but these interactions are weakened with
forward flight
• Full scale nozzle diameter did not have a significant
effect on twin jet EPNL calculations
• Twin jet effects can account for up to a 5 EPNdB
difference between in-plane and out-of-plane
measurements
• For a horizontal twin jet configuration, the single jet
plus 3 EPNdB estimation would be sufficient for the
lateral microphone at any of the jet spacings tested
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