Workshop on Jet Exhaust Noise Reduction for Tactical Aircraft - NASA Perspective
Dennis L. Huff
NASA Glenn Research Center
and
Brenda S. Henderson
NASA Langley Research Center
Jet noise from supersonic, high performance aircraft is a significant problem for takeoff and landing operations near air
bases and aircraft carriers. As newer aircraft with higher thrust and performance are introduced, the noise tends to
increase due to higher jet exhaust velocities. Jet noise has been a subject of research for over 55 years. Commercial
subsonic aircraft benefit from changes to the engine cycle that reduce the exhaust velocities and result in significant
noise reduction. Most of the research programs over the past few decades have concentrated on commercial aircraft.
Progress has been made by introducing new engines with design features that reduce the noise.
NASA has recently started a new program called “Fundamental Aeronautics” where three projects (subsonic fixed
wing, subsonic rotary wing, and supersonics) address aircraft noise. For the supersonics project, a primary goal is to
understand the underlying physics associated with jet noise so that improved noise prediction tools and noise reduction
methods can be developed for a wide range of applications. Highlights from the supersonics project are presented
including prediction methods for broadband shock noise, flow measurement methods, and noise reduction methods.
Realistic expectations are presented based on past history that indicates significant jet noise reduction cannot be
achieved without major changes to the engine cycle. NASA’s past experience shows a few EPNdB (effective
perceived noise level in decibels) can be achieved using low noise design features such as chevron nozzles. Minimal
thrust loss can be expected with these nozzles (< 0.5%) and they may be retrofitted on existing engines. In the long
term, it is desirable to use variable cycle engines that can be optimized for lower jet noise during takeoff operations
and higher thrust for operational performance. It is also suggested that noise experts be included early in the design
process for engine nozzle systems to participate in decisions that may impact the jet noise.
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Workshop on Jet Exhaust NoiseReduction for Tactical Aircraft
- NASA Perspective
November 27, 2007
by Dennis L. Huff and Brenda S. Henderson
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Good News: High performance military aircraft noise isdominated by a single source called “jet noise”(commercial aircraft have multiple sources)
Bad News: This source has been the subject of resear chfor the past 55 years and progress has beenincremental.
• Major jet noise reduction has been achieved through changingthe cycle of the engine to reduce the jet exit velo city.
• Smaller reductions (a few EPNdB) have been achieved usingsuppression devices like mixing enhancement, acoust ic liners.
• Significant jet noise reduction without any perform anceloss is probably not possible!
History Shows The Problem Is Difficult To Solve
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777-200
A330-300
MD-90-30
MD-11
A320-200
747-400
A300-600R
767-300ERA310-300757-200
MD-87MD-82
B-747-300A300B4-620
A310-222
MD-80
B-747-200
B-747-SPDC-10-40
B-747-200
A300
B-747-200
B-747-100
B-737-200B-737-200
B-727-200DC9-10
B-727-100
B-727-100
20.0
-10.0
0.0
10.0
1960 1970 1980 1990 2000 2010 2020Year of Entry (Approximate)
Average NoiseLevel Relativeto Stage 3(EPNdB)
Stage 2
Stage 3
Stage 4
Averagein Service
Aircraft Noise Trends
F15
F16
F14
F18Military, After BurnerMilitary, Dry
NASA Technology Goal(-42 dB Cum)
B-737-800B-737-900
A320-232
A340-541
A318-112
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Supersonic Jet Noise Sources
Tam, C.K.W., Directional Acoustic Radiation From a Supersonic Jet Generated by Shear LayerInstability, Journal of Fluid Mechanics , Vol. 46, Pt. 4, Apr. 27, 1971, pp. 757-768.
• Turbulent Jet Mixing• Broadband Shock Noise• Screech
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Recent NASA Noise Reduction Research Programs
High Speed Research (HSR) Program• 1990 - 1999• Focused research on specific engine & mission (mixe d-flow turbofan)
Advanced Subsonic Technology (AST) Noise Reduction Program• 1993 - 2001• Applied research for commercial turbofan engines wi th emphasis
on fan and jet noiseQuiet Aircraft Technology (QAT) Project
• 2001 - 2005• Research for new subsonic commercial engines to mee t aggressive 10 dB
and 20 dB noise reduction goals (relative to 1997 b est-in-fleet technology)Fundamental Aeronautics (FA) Program
• 2006 - present• Supersonic & subsonic fundamental research aimed at understanding
noise sources, also working on rotorcraft noise• Emphasis on Multi-Disciplinary Design and Optimizat ion (MDAO) tool
development
Noise research for subsonic applications outpaces supersonic work by a large margin!
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NASA Lear 25 Flight Demonstrationof Turbojet Noise Reduction
Objectives
• Confirm model scale test results• Determine flight effects of installed
chevron nozzle• Investigate chevron nozzles for
supersonic jet exit velocities
6 and 12 Point Chevron Nozzles
Approach• Completed model scale acoustic and
performance tests • Demonstrated 3 EPNdB jet noise
reduction with 0.5% thrust loss• Flight test in March 2001 on
Learjet 25 with CJ610-6 enginesshowed ~2 EPNdB jet noise reduction
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NASA Lear 25 Flight Demonstrationof Turbojet Noise Reduction
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NASA’s Fundamental Aeronautics Program
Overcome today’s national challenges in air transpo rtation
• Invest in fundamental core competencies
• Involve external aeronautics community to support b est technological talent and ideas
• Widely disseminate research results
Four projects
• Subsonic Fixed Wing
• Subsonic Rotary Wing
• Supersonics
• Hypersonics
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Supersonics Project
Major technical challenges• Efficiency
• Environment
•Airport noise
•Sonic boom
•High-altitude emissions
• Performance
• Entry descent and landing
• Multidisciplinary design, analysis, and optimization
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• Enable vehicles capable of economical supersonic flight to be acoustically compatible with existing fleet around airports.
• Envision noise reduction technologies which break current overall noise trends of noise vs specific thrust.
• Create design and analysis tools to evaluate and optimize noise along with other aircraft performance measures.
Airport Noise - Technical Challenge
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Airport Noise - Technical Approach
•Elements
– Prediction
– Diagnostics
– Engineering
•Significant interaction between elements
• Internal and external NASA Research Announcement (NRA) research folded into program to meet project objectives
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Prediction
•Statistical modeling in supersonic jet noise
– Mixing noise, shock noise, and Mach wave emission
•Time-resolved CFD/CAA for jet aeroacoustics
– LES for non-compact sources, LEE for complex propagation in shocked flow
•Assessment of supersonic noise prediction tools
– Empirical, statistical, and time-resolved codes
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90
85
80
75
70
65
60
55 10.00 5.00 1.00 0.50 0.10 0.05 0.01
70 deg
Strouhal number
SP
L -
10 L
og (
A)
- 52
.5 L
og (
Vj/a
), d
B
Tt / Ta = 3.2
M=1.38
• No method exists to predict broadband shock-associated noise for general jet geometries and conditions
• Acoustics and flow-field measurements to be performed at small and moderate scale
• Steady RANS flow simulation coupled with source modeling based on measured unsteady flow properties will provide noise prediction
• Separation of shock-associated noise from other jet noise sources accomplished using new empirical method
• Close collaboration between Penn State, Boeing and NASA – good progress in all sub-tasks
Schlieren image of jet shock cell structure
RANS predictions of shock-containing jets
Separation of mixing and shock noise
Shock noise
Mixing noise
Prediction and Measurements of Broadband Shock-Associated Noise
PI: Philip J. Morris, Penn State U.
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Diagnostics
•Phased array diagnostics for source distribution
– Combine flow and acoustic array measurements
•Turbulence statistics for noise prediction codes
– Mixing noise, shock noise, Mach wave emission
•Supersonic aeroacoustic database
– Far-field noise and source distribution for range of geometries (dual stream, round, rectangular, twin)
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JES
Linear ArrayPhased Array
Wall Mic
LSAWT Phased Array Experiment
• Detailed source distribution maps obtained for subsonic and supersonic jets using conventional beamforming
• Next step - DAMAS deconvolution to resolve shock noise source distribution in plume
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Application of Time-Resolved PIV to Supersonic Hot Jets
Advanced turbulent velocity measurements yield space-time statistics required to model jet noise sources and validate CFD-based prediction codes.
NASA Glenn AeroAcoustic Propulsion Lab
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S-DuctY-Duct
Angle Adapter
Twin Jet
Investigate• Jet plume interactions• Noise characteristics of
rectangular nozzles
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Engineering
•Broadband shock noise reduction through shock modifications
– Air injection
•Offset stream nozzles for noise reduction
•Unsteady actuator for time-dependent jet control
– LES-optimized temporal control of jet instabilities and medium-scale testing
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Strategic Environmental Research & Development Program
Investigate• Noise characteristics of
realistic nozzle geometries• Impact of bypass flow on
acoustic radiation and noise reduction devices
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Air Injection
Noise reduction can be achieved in single and dual stream jets
Fan Nozzle Core Fluidic Chevron Nozzle
Air Supply
30
40
50
60
70
80
90
100 1000 10000 100000Frequency (Hz)
SP
L (d
B)
IPR = 1.0IPR = 2.0IPR = 4.0
NPRc = 2.17
θ = 61o
40
50
60
70
80
90
100
100 1000 10000 100000
Frequency (Hz)
SP
L (d
B)
IPR = 1.0
IPR = 2.5
IPR = 4.0
NPRc = 1.61
NPRf = 2.23
θ = 61o
Shock Noise
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Realistic Expectations
• With history as a guide, don’t expect this problem to be solved soon.
• High performance aircraft cannot rely on engine cyc le benefits the waycommercial aircraft have met large noise reduction targets.
• Commercial aircraft have benefited from sustained n oise reductionresearch. This has not been done for high performa nce aircraft engines,which means the foundation for this research is les s mature.
• Small reductions in jet noise (a few EPNdB) are exp ected to be possible withsmall performance penalties (< 0.5%). Retrofitable solutions may be possible(i.e. Chevron Nozzles).
• Large reductions in noise will require a long-term research commitment andconsideration for noise during initial design of en gine. Variable cycleengines are needed to make significant progress.
• Modified aircraft operations for noise abatement is a good solutionfor community noise problems. Barriers, acoustic e nclosures, and earprotection are the most practical solutions for nea r field noise problems.
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(Back-Up Slides)
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Pinker, R.A., “A Brief Review of the Source Noise TechnologyApplicable to Fixed-Wing Military Aircraft”, AGARD- CP-512, Combat Aircraft Noise, 1991)
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Highlights From NASA’s HSR Program
Noise research focused on improving low bypass rati o turbofans with variablegeometry mixer-ejector nozzles
• Mixer on primary flow reduces low frequency jet noi se• Acoustic liners absorb high frequency noise• Fan inlet noise issue during approach, addressed th rough improved design
Major Technology Improvements
• Better mixer designs aided by 3-D CFD (reduced thru st loss)• Improved acoustic liners (higher temperature, lower weight)• Technology available to provide engine that can mee t commercial
certification requirements (Stage III with ~2-4 dB margin => Stage IV)• Improved materials technology beat original engine weight goals
Jet noise reduction achieved, but required heavy mixer-ejector nozzle
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High-Speed Civil Transport Jet NoiseModel Test Data Projections
Gross Thrust Loss
PRE 1972TECHNOLOGY
(SST)
POST 1990TECHNOLOGY
(HSCT)
Sid
elin
e N
oise
Sup
pres
sion Des
ired tr
end
Projections
1/2-Scale Model data
1/7-Scale Model data
GOAL
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F-15 ACTIVE ACOUSTIC FLIGHT TESTEFFECTS OF FLIGHT SPEED ON JET NOISE
Fully expanded Mach number M j = 1.45 Nozzle exit Mach number M e = 1.73
Upstream OASPLdominated by jetbroadband shocknoise, increases with aircraft Machnumber by factor
5.2)cos1( −− ψfM
Downstream OASPLdominated by jet mixing noise,decreases with aircraft speed by factor 5)( fj VV −
ShockNoise
MixingNoise
angle from inlet ψ°ψ°ψ°ψ°
OA
SP
L at
sou
rce,
dB
Mf = .77
Mf = .61
Mf = .46
Mf = .34
From T. Norum, NASA Langley Research Center
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Higher Bypass Ratio Swept/Leaned StatorsScarf Inlets
Act ive Vanes Installed on the NASA,Glenn Act ive noise Cont rol Fan
Rotor Blade
Stator Vane
Active Noise ControlNoise PredictionChevron Nozzles
Forward-Swept Fans
Highlights From NASA’s Subsonic Research