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Environment
Introduction
Environment-Aircraft Noise Reduction
Noise impact of subsonic aircraft is constraining the air transportation
system through curfews, noise budgets and slot restrictions. Evidence of
this problem is already common. The travelling public is familiar with
airport operational restrictions (e.g., curfews) resulting from
community noise concerns. The ever increasing international aircraft
noise stringency standards have mandated phase-out of stage 2 airplanes
by the year 2000, and the number of airports affected by local noise
restrictions has grown from 119 airports in 1980 to 595 in 1998
worldwide.
The 1995 White House National Science and Technology Council report,
Goals for a National Partnership in Aeronautics Research and Technology,
states that, "Environmental issues are likely to impose the fundamental
limitation on air transportation growth in the 21st century." These
noise issues are also inhibiting expansion or construction of new
facilities. Furthermore, EPA has established that a Day-Night Average
Level of 55 decibels is "requisite to protect the public health and
welfare with an adequate margin of safety." In the best interest of our
nation, the FAA and NASA vision includes a noise- constraint-free air
transportation system. This will benefit the public in terms of
increased quality of life and readily available and affordable air
travel, and our aviation industry will enjoy continued global
leadership.
The goal of the Noise Reduction Program, in cooperation with U.S.
industry, is to provide technology to allow unrestricted market growth,
while complying with international environmental requirements. The
objective is to "Reduce the perceived noise levels of future aircraft by
a factor of two (10 decibels) relative to 1997 subsonic aircraft within
10 years and by a factor of four (20 decibels) within 25 years."
NASA's objective of 20-decibel reduction in noise will contain the
55-decibel noise contour and the objectionable noise within the
boundaries of most airports, thereby enabling the airport operations
necessary to address the growing capacity demands of the American
public. The goal will be achieved via systematic development and
validation of noise reduction technology in three areas: engine system,
aircraft system, and operational procedures. The strong coordination
among Government, industry and academia will continue to effectively
transition noise reduction technology to the U.S. industry.
Fan Noise Reduction
An engine fan noise reduction of 3 decibels was achieved with an
innovative, low-noise stator design. This design has the potential to
effectively eliminate fan tone noise as a significant contributor to
community noise. This is a tremendous achievement in that it
accomplishes what fan tone noise research over the past 30 years had not
yet produced. With the new stator, engine designers can direct more
attention to reducing fan broadband noise.
Swept and Leaned Stator Model
The 3-decibel fan noise reduction was met through a combination of a
low-noise fan design and cycle changes, which were validated in
high-fidelity scale-model engine simulator tests in wind tunnels. The
tests clearly demonstrated the achievement of the 3-decibel fan noise
reduction. Engines designed to take advantage of this innovation will
represent a new paradigm in engine design and will open the door for the
application of additional engine-noise reduction concepts.
NASA POC:
Dennis Huff
216-433-3913
Dennis.L.Huff@grc.nasa.gov
Jet Noise Reduction
High-fidelity wind tunnel scale-model tests of advanced exhaust mixers
have shown jet noise reduction of 3 decibels for a range of engine
types, including separate flow engines. The mixers are exhaust nozzles
that have been formed into complex shapes designed to enhance the mixing
of the core, bypass, and ambient airflows to reduce jet noise. Although
mixers have been in use, the innovation in these results was an improved
design method, which incorporated numerically predicted flow physics to
guide the noise reduction design and optimize engine performance. Such
methods expand the understanding of the noise source mechanisms and
ultimately extend the benefit of the developed technology to many
different applications. In addition to these scale-model test results, a
3-decibel jet noise reduction was also achieved in an Allied-Signal
static test of a full-scale engine. The developed technology is being
considered in industry designs and will likely be on production engines
early next century.
Model Jet Noise Reducing Advanced Exhaust Mixer
NASA POC:
Dennis Huff
216-433-3913
Dennis.L.Huff@grc.nasa.gov
Liner Acoustics
Jet engine nacelles or cowlings are equipped with liners to partially
absorb fan tones before they propagate outside the engine. Typical
liners today reduce community noise impact by 4 dB. The goal of NASA
research is to improve this by another 2 decibels. Recent research
results have affected the whole liner design process, from determining
the optimal acoustic properties of the liner, which must operate in the
extreme flow conditions inside an engine, to validating that the desired
properties have been achieved. The improved design process was validated
in a wind tunnel test of a high-powered model fan where half of the
goal, or a 1-decibel liner improvement, was achieved. Model and engine
static tests are in progress to validate other innovations with the
potential to achieve the full goal.
Advanced Nacelle Wind Tunnel Model
NASA POC:
Dr. Joe Posey
757-864-7686
J.W.Posey@larc.nasa.gov
Airframe Noise Reduction
During an aircraft approach, the noise the community hears is more than
just the engine. Airplanes take off and land at slow speeds of 140 to
180 knots, compared with cruise speeds of 550 knots. To ensure adequate
lift and stall margin during the critical take-off and landing, wings
are enhanced with such lift-enhancing systems as trailing-edge flaps and
extendible slats on the wing leading edge. The exposed edges and gaps of
these high lift systems, not to mention the deployed landing gear,
create airframe noises that can be as loud as the engines.
Flap Airframe Noise Model in Wind Tunnel
NASA has developed a flow-physics-based technology that reduces the
noise created by the air passing over flap edges. This technology is a
micro piece of hardware that can be easily added to existing airplanes.
The technology has been validated in small-scale-model tests and
full-scale numerical simulation. Flap airframe noise reductions of 4
decibels have been demonstrated experimentally with little degradation
in lift performance. Adoption of this technology can not only benefit
the community but also aid the airline industry in meeting the more
stringent noise certification standards of the future.
NASA POC:
Dr. Michele Macaraeg
757-864-2295
M.G.MACARAEG@larc.nasa.gov
Interior Noise Reduction
Low interior noise is critical to passenger comfort and acceptance of
air travel, particularly for new vehicles like the civil tiltrotor or
other nontraditional commercial transports. A multidisciplinary
(structures and noise together) approach taken in NASA research has lead
to innovations that will enable future aircraft to be designed with
inherently quiet interiors, rather than with today's approach of
controlling interior noise after the airplane structure is designed.
Interior Noise Control Flight Demonstration
The progress to date centers on three areas: (1) source identification,
(2) design optimization and (3) noise control technology. New design
approaches have, by optimizing both the primary structure and passive
noise control treatments, reduced aircraft noise by 5 decibels. Further,
active noise control has been demonstrated to reduce the interior
propeller tone noise in a Raytheon/Beech 1900D by 6 decibels. Current
research is focused on boundary-layer and jet noise sources where
significant broadband reductions have been attained in wind tunnel
tests. Your future conversations during air travel will be at whisper
level, allowing you and your neighbors to fully enjoy your flight.
NASA POC:
Dr. Rich Silcox
757-864-3590
R.J.Silcox@larc.nasa.gov
Environment
Introduction
Environment-Aircraft Emissions Reduction
The International Civil Aviation Organization (ICAO) Committee on
Aviation Environmental Protection is voicing worldwide concerns about
local air quality and climate change. The Kyoto Protocol to the UN
Framework Convention on Climate Change has drawn growing attention to
aviation's emissions of carbon dioxide (CO2), in particular. A special
report on aviation and the global atmosphere, to be published by the
Intergovernmental Panel on Climate Change (IPCC) in September 1999, will
delineate aviation's impact on climate.
International agencies are considering additional nitrogen oxides (NOx)
reductions at take-off and possibly during cruise and NOx limits so
stringent that emissions fees or limited access to some countries could
result. Recent observations of aircraft contrail behavior have brought
growing concern over aerosol, particulate, and sulfur levels, which are
suspected of producing high altitude cirrus clouds that adversely affect
Earth's climate. Furthermore, stringent ozone and particulate matter
standards under the U.S. Clean Air Act have resulted in local
authorities and environmental interest groups demanding action from
Federal agencies and the air carriers to reduce emissions of NOx (which
as suspected to contribute to toxic ozone production) and other
pollutants.
Thus, continued scientific assessment and development of safe and
affordable technology options for reducing aircraft engine emissions are
important to protect the environment and to sustain the growth of
aviation. Proposed research and technology objectives are to reduce NOx
emissions by a factor of three within 10 years and by a factor of 5
within 25 years. The program will focus on developing low emissions,
efficient combustors operating at high pressure ratios and temperatures,
while maintaining high levels of operability and maintainability.
Overall engine efficiency and related CO2 improvements will also be
sought, for example, through performance improvements and weight
reductions resulting from fewer compressor stages, advanced materials,
and supporting subsystems.
In the global picture, it is in everyone's best interest to
ensure a clean
environment for future generations.
Atmospheric Effects of Aviation Project (AEAP)
Commercial aviation produces primary combustion products, carbon dioxide
(CO2) and water vapor (H2O), at a level comparable to its expenditure of
fossil fuels, about 3 percent of global fuel consumption. Unlike
ground-based combustion sources, aircraft deposit their combustion
products at much higher altitudes, into the upper troposphere and lower
stratosphere (25,000 to 50,000 feet). Combustion byproducts deposited
there can have long residence times, enhancing their impact. The
apparent increased incidence of cirrus clouds and persistent contrails
are visible examples of these effects. The major objective of AEAP is to
provide periodic assessment of the impact of cruise altitude aircraft
emissions on ozone change in the upper atmosphere and climate change,
such as the impact of increased cirrus cloud cover on global warming.
The AEAP combines atmospheric research and aviation technology
development in focused laboratory, modeling, and field mission
studies.
NASA POC:
Richard J. Lawrence
301-286-1022
rlawrenc@pop400.gsfc.nasa.gov
Web Site:
http://hyperion.gsfc.nasa.gov/AEAP/
Ultra Efficient Engine Technology Program
The Ultra Efficient Engine Technology Program is being planned by NASA
to develop high-risk, high-payoff technologies that will dramatically
increase turbine engine performance and efficiency. Improved fuel
efficiency reduces CO2, but objectives will also be to significantly
reduce NOx emissions. For the latter, the program goal is to develop
component technology that will reduce NOx emissions by 70 percent from
1996 ICAO standards for take-off and landing conditions and also to
develop combustor technology that will reduce NOx emissions to
no-ozone-impact levels during cruise.
Carbon dioxide reduction is directly proportional to the amount of fuel
burned. The efficiency goals for a reduction of CO2 by at least 8
percent could mean engine operations at pressure ratios as high as 55
and turbine inlet temperatures of 3100¡ F. Thus technologies must be
developed for such high temperature turbomachinery components, materials
and structures, and novel concepts for significantly improved propulsion
airframe integration through advanced technology concepts. These will
provide the dramatic increases in efficiency and reductions in CO2.
These technologies can also lead to weight reductions such as reducing
the number of compression and turbine stages from today's baseline
engines.
NASA POC:
Peter G. Batterton
216-433-3912
Peter.G.Batterton@grc.nasa.gov
Low NOx Emissions Technology
Experimental and analytical research to advance the understanding of
emissions formation in combustion processes in advanced engine cycles
have been the focus of the environmental elements of the Advanced
Subsonic Technology and High Speed Research programs. Engine emittants
include oxides of nitrogen, speciation of hydrocarbons (CO, CO2, and
UHC, etc.) and sulfur oxides, and carbon-based gaseous or liquid
particulates. Experimental work includes advanced low-emission low-cost
fuel injectors, advanced diagnostics for emission characterization, and
advanced chemical kinetic and aerosol (particulates) measurement
techniques. Analytical work includes the development of analytical
models for turbulence-chemistry interaction, supercritical spray, and
radiation.
Large engine emissions program-TAPS Mixer/Combustor
In collaboration with the U.S. industry, NASA has contributed to the
advancement of low-emission combustion systems for aircraft engines. A
50 percent reduction in NOx emissions, compared with 1996 ICAO baseline,
has been demonstrated in sector combustors for advanced subsonic
engines at NASA. A 90 percent reduction in NOx emissions, compared with
today's production engines, has been demonstrated in sector combustors
for supersonic engines at General Electric. These advanced combustor
technologies include lean direct injection for subsonic engines and lean
premixed, prevaporization for supersonic engines.
NASA POC:
Dr. Chi-Ming Lee
216-433-3413
Chi-Ming.Lee@grc.nasa.gov
Ceramic Matrix Composite (CMC) Combustor Liner
This CMC material has demonstrated a greater than 9000-hour life
at
2200 degrees Fahrenheit in laboratory test cycles typical of aircraft
engines.
Combustor concepts for low NOx emission require that there be little or
no film air cooling of the liner. This means high operating
temperatures. The combustor life goal of 9000 hot hours is a major
durability challenge. NASA's High Speed Research (HSR) program has
developed an advanced silicon-carbide-fiber-reinforced silicon carbide
(SiC/SiC) CMC as liner material for a low NOx combustor. Various
enabling technologies contributed to the successful development of a CMC
liner material. These include development of (1) advanced silicon
carbide fiber with high-temperature stability, (2) new fiber coating,
(3) new fabrication technique for producing dense composites, and (4)
environmental barrier coating for preventing surface recession. Further
development of CMC liners for higher temperature and pressure
capabilities will lead to applications in a wide range of low-emission
combustor designs, including subsonic aircraft.
NASA POC:
Dr. Ajay K. Misra
216-433-8193
Ajay.K.Misra@grc.nasa.gov
Adaptive Performance Optimization
NASA on-board software, called Adaptive Performance Optimization,
minimizes drag and saves fuel through small movements of outboard
ailerons in cruise flight. These movements give the aircraft's wings the
most efficient, or optimal, airfoil shape. Reduction of drag can have a
major impact on airline profit margins: For wide-body transports, a 1
percent reduction in drag could save $140,000 per aircraft per year in
fuel cost. Many aircraft must fly with less than a full payload because
of factors like route length, higher than normal airport altitude (e.g.
Denver), and hot summer temperatures. For these aircraft, a 1 percent
reduction in drag can be used to trade payload for fuel that can be
worth up to $4,000,000 in increased revenue per aircraft per year.
Elements of an Adaptive Performance Optimization system.
NASA POC:
Glenn Gilyard
805-258-3724
glenn.gilyard@dfrc.nasa.gov
Electrically Powered Actuators
Three advanced, electrically powered actuators, flight validated on a
NASA F-18, will lead to more-electric future aircraft designs, reducing
reliance on an aircraft's central hydraulic system.
Adopting electrically powered actuators for all flight control surfaces
could lead to a 5 to 9 percent fuel savings on an all-electric passenger
plane and a 30 to 50 percent reduction in ground equipment. A follow-on
version of one of the actuators is being used on the spaceflight-rated
X-38 Crew Return Vehicle technology demonstrator and is being developed
for the X-33 reusable launch vehicle technology demonstrator. Electric
actuators are being considered for the primary flight control surfaces
on a Joint Strike Fighter candidate as well.
Systems Research Aircraft/Electric Actuator
Partners in the Electrically Powered Actuation Design program were the
Air Force Research Laboratory, the Naval Air Warfare Center Aircraft
Division, and NASA.
NASA POC:
John Sharkey
805-258-3965
Unleaded Fuels Program
As a result of the mandates of the 1990 Clear Air Act, the FAA initiated
unleaded fuel research and engine and fuel testing. Such testing is
being conducted in cooperation with an FAA and industry established
Coordinating Research Council (CRC) Committee to address issues such as
engine detonation, material compatibility, volatility (vapor lock),
engine performance, storage stability, water reaction, emissions, fuel
consumption changes, and durability (engine and component life).
Engine and fuel tests are currently being conducted to validate the
octane requirement that is acceptable for engines within the existing
general aviation fleet. At the conclusion of these tests, minimum octane
requirements for candidate unleaded fuel formulations will be specified
as a development goal for participating oil companies within the CRC
Committee. The FAA will then evaluate these fuels through a series of
performance and safety related engine fuel tests.
Data from these tests will aid the FAA in certifying the existing fleet
of general aviation aircraft on a replacement fuel and in developing a
specification with the American Society of Testing and Materials (ASTM)
for an unleaded aviation gasoline to replace the currently available 100
octane low-lead fuel. This specification, in turn, will serve as a basis
for the development of advisory material covering the certification of
new piston powered engine designs and their application to the
performance of new general aviation airplanes. Further testing at the
FAA's small-engine test facilities is anticipated to define the safety
and performance of other critical in-service aircraft engines that have
not been tested with the newer unleaded fuels, as well as to develop
other new or alternate fuels.
FAA POC:
Stewart Byrnes
609-485-4499
stewart.byrnes@faa.gov
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