National Aeronautics and Space Administration
Small Business Innovation Research 2001 Program Solicitation

TOPIC A3 Environmental Compatibility: Noise and Emissions

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A3.01 Airframe Systems Noise Prediction and Reduction
A3.02 Propulsion System Emissions and Noise Prediction and Reduction

NASA has very aggressive goals for providing technologies that will ensure the noise and emissions environmental compatibility of future commercial aircraft. In particular, the noise goals are to reduce the perceived noise levels of future aircraft by a factor of two (10 EPNdB) within 10 years of 1997, and a factor of four (20 EPNdB) within 20 years. The emissions goals are to reduce aircraft emissions by a factor of three within 10 years and a factor of five within 20 years. These goals are necessary to meet increasingly stringent local, national, and international noise and emission regulations while enhancing operating safety and productivity and increasing aviation system throughput. Accomplishment of these goals will require revolutionary airframe and propulsion technologies to be developed and handed off to the aerospace community in a timely fashion. Particular areas of interest are: (1) Noise prediction and reduction technologies for propulsion source noise, nacelle aeroacoustics, airframe noise, and noise minimal flight procedures for future subsonic and supersonic commercial aircraft. (2) Aircraft interior noise reduction technologies to improve passenger and crew comfort. (3) Emissions reduction technologies for ultra low NOx emissions combustor concepts which also reduce the aerosol and particulates emissions. (4) Innovative airframe and propulsion concepts relative to these goals.

A3.01 Airframe Systems Noise Prediction and Reduction
Lead Center: LaRC
Participating Center(s): None

Innovative technologies and techniques are necessary for the introduction of efficient, environmentally acceptable airplanes, rotorcraft and advanced aerospace vehicles. Improvements in noise prediction and control technologies are needed for jet, propeller, rotor, fan, turbomachinery, and airframe noise sources to reduce the impact on community residents, aircraft passengers and crew, and launch vehicle payloads. Innovations in technologies and algorithms for the following specific areas are solicited:

• Fundamental and applied computational fluid-dynamics techniques for aeroacoustic analysis, particularly for use early in the design process.
• Simulation and prediction of aeroacoustic noise sources particularly for airframe noise sources and situations with significant interactions between airframe and propulsion systems.
• Innovative active and passive acoustic treatment concepts for engine nacelle liners.
• Technologies for active and passive control of aeroacoustic noise sources for Blended Wing Body and other advanced aircraft.
• Reduction technologies and prediction methods for rotorcraft and advanced propeller aerodynamic noise.
• Computational and analytical structural acoustics techniques for aircraft and advanced aerospace vehicle interior noise prediction, particularly for use early in the airframe design process.
• Technologies and techniques for active and passive interior noise control for aircraft and advanced aerospace vehicle structures.
• Prediction and control of high-amplitude aeroacoustic loads on advanced aerospace structures and the resulting dynamic response and fatigue.
• Development and application of flight procedures for reducing community noise impact of rotorcraft and future subsonic and supersonic commercial aircraft while maintaining safety, capacity and fuel efficiency.
  

A3.02 Propulsion System Emissions and Noise Prediction and Reduction
Lead Center: GRC
Participating Center(s): None

Emissions: Current environmental concerns with subsonic and supersonic aircraft center around global warming and the impact on the Earth's climate and, if not addressed, may threaten future market growth. Carbon dioxide (CO₂) and oxides of nitrogen (NOx) are the major emittants of concern coming from commercial aircraft engines. CO₂ is a greenhouse gas which may impact the warming of the Earth's climate. NOx emissions can destroy ozone in the upper atmosphere which protects humans from harmful uv radiation from the Sun and NOx can produce ozone in the lower atmosphere. Around airports, it appears as smog and causes breathing and health problems. Current state-of-the-art engines and combustors in most subsonic aircraft are fuel efficient and meet the 1996 ICAO NOx limits. The Kyoto Agreement is applying pressure for additional CO₂ reductions, and Europe and the U.S. Environmental Protection Agency are applying pressure for additional NOx reductions at takeoff and possibly cruise conditions. Stringent CO₂ and NOx limits could result in emissions' fees or limited access to some countries. Also, recent observations of aircraft exhaust contrails (from both subsonic and supersonic flights) have resulted in growing concern over aerosol, particulate, and sulfur levels in the fuel. In particular, aerosols and particulates from aircraft are suspected of producing high altitude clouds which could adversely affect the Earth's climatology. NASA has set some very aggressive goals for reducing emissions of future aircraft by a factor of three within 10 years and by a factor of five within 20 years. Advanced concepts research for reducing CO₂ and NOx, and analytical and experimental research in characterization (intrusive and non-intrusive) and control (through component design, controls, and/or fuel additives) of gaseous, liquid and particulates of aircraft exhaust emissions is sought. Specific aircraft operating conditions of interest include the landing-takeoff cycle as well as the in-flight portion of the mission. Areas of particular interest are:

• New concepts for reducing carbon dioxide, oxides of nitrogen (NO, NO₂, NOx), unburned hydrocarbons; carbon monoxide, particulate, and aerosols emittants (novel propulsion concepts, injector designs to improve fuel mixing, catalysts, additives, etc.);
• New fuels for commercial aircraft which minimize carbon dioxide emissions;
• Innovative active control concepts for emission minimization with an integrated systems focus including emission modeling for control, sensing and actuation requirements, control logic development, and experimental validation are of interest; and
• New instrumentation techniques are needed for the measurement of engine emissions such as NOx, SOx, HOx, atomic oxygen and hydrocarbons in combustion facilities and engines. Size, size distributions, reactivity, and constituents of aerosols and particulates are needed, as are temperature, pressure, density, and velocity measurements. Optical techniques that provide 2-D and 3-D data; time history measurements; and thin film, fiber optic, and MEMS-based sensors are of interest.

Noise: NASA intends to provide enabling technologies to reduce the perceived noise levels of future aircraft by a factor of two (10 EPNdB) from 1997 technology aircraft by 2007, and a factor of four (20 EPNdB) by 2022. These goals are necessary to meet increasingly stringent local, national and international community noise regulations while enhancing operating safety and productivity and increasing aviation system throughput. Engine noise reduction technologies are required in the areas of propulsion source noise, nacelle aeroacoustics, and engine/airframe integration. These aggressive aircraft noise reduction goals will require revolutionary advances in propulsion technologies. Some of the key technologies needed to achieve these goals are revolutionary propulsion systems for reduced noise without significant increases in cost and emissions. Noise reduction concepts need to be identified that provide economical alternatives to conventional propulsion systems. NASA is soliciting proposals in one or more of the following areas for Propulsion System Noise Reduction:

• Innovative acoustic source identification techniques for turbomachinery noise. The technique shall be described and demonstrated on a relevant source. A simple source may be used where the solution is known to demonstrate the technique. A clear explanation on how the technique can be applied to turbofan engines should be included. The technique should be capable of identifying sources contributing to dominant engine components, such as fan and jet noise. Fan Noise: The technique shall be capable of separating fan sources such as fan-alone versus fan/stator interaction for both tones and broadband noise. Sufficient resolution is needed to determine the location of the dominant sources on the aerodynamic surfaces. Jet Noise: The technique shall be capable of locating both internal and external mixing noise for dual-flow nozzles found in modern turbofans.
• Innovative turbofan source reduction techniques. Methods shall emphasize noise reduction methods for fan, jet and core components without compromising performance for turbofan engines. A resulting engine system that incorporates one or more of the proposed methods should be capable of reducing perceived noise levels anywhere from 10 to 20 EPNdB relative to FAR 36, Stage 3 certification levels.

Advanced Materials for Reduced Emissions: Proposals are also sought to address advanced materials, their development, and their application to primary propulsion systems such as aircraft gas turbines, rocket and turbine based combined cycle engines, and rocket engines as well as auxiliary power sources in aircraft and space vehicles. Materials of interest include any especially used in propulsion systems such as high temperature polymers, nickel base alloys, ceramic matrix composites, coatings for these, and processes for their economical and reliable preparation.

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