National Aeronautics and Space Administration
Small Business Innovation Research 1999 Program Solicitation

TOPIC 02 Subsonic Transport Environmental Compatibility

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02.01 Aircraft Noise Prediction and Reduction
02.02Propulsion System Noise Prediction and Reduction
02.03Subsonic Aircraft Systems Emissions Reduction

NASA has very aggressive goals for ensuring the noise and emission environmental compatibility of future aircraft. They are to reduce the perceived noise levels of future aircraft by a factor of two (10 EPNdB) within ten years, and a factor of four (20 EPNdB) within 20 years and to reduce emissions of future aircraft 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. Noise prediction and reduction technologies are required in the areas of propulsion source noise, nacelle aeroacoustics, airframe noise, and noise minimal flight procedures for jet and propeller airplanes and rotorcraft. In addition, aircraft interior noise reduction technologies are required to improve passenger and crew comfort. Emissions reduction technologies are required for a number of aerosols and particulates including nitrogen oxides, sulfur oxides, carbon dioxide, and water vapor.

02.01 Aircraft Noise Prediction and Reduction

Innovative noise reduction concepts, techniques, and methods are needed for the design and development of efficient, environmentally acceptable airplanes and rotorcraft. Improvements in aircraft noise prediction and control are needed for jet, propeller, rotor, fan, turbomachinery, and airframe noise sources for community residents, aircraft passengers and crew. Innovations in the following specific areas are solicited:

• Fundamental and applied computational fluid-dynamics techniques for aeroacoustic analysis, particularly for use early in the design process.
• Reduction concepts and prediction methods for jet noise of subsonic, supersonic, and hypersonic aircraft.
• Concepts for active and passive control of fan, turbomachinery, and jet noise in engine nacelles.
• Reduction concepts and prediction methods for rotorcraft and advanced propeller aerodynamic noise.
• Simulation and prediction of aeroacoustic noise sources including airframe noise and propulsion-airframe integration.
• Computational and analytical structural acoustics techniques for aircraft interior noise prediction, particularly for use early in the airframe design process.
• Concepts for active and passive interior noise control for aircraft.
• Prediction and control of high-frequency aeroacoustic loads on advanced aircraft structures and the resulting dynamic response.

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02.02 Propulsion System Noise Prediction and Reduction

NASA's aggressive subsonic aircraft noise reduction goals will require revolutionary advances in propulsion technologies. Some of the key technologies needed to achieve these goals are fast, highly accurate computational acoustic methods, advanced source identification techniques, and revolutionary propulsion systems for reduced noise and low cost. Advanced computational methods are needed that can both model the relevant flow physics and be used in a design environment. Source identification techniques are needed for both wind tunnel model scale tests and full scale static engine tests to determine the locations of the disturbances that contribute to the overall engine noise levels. It is anticipated that revolutionary noise reduction concepts will be needed to achieve future subsonic noise reduction goals. Therefore, advanced 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 Prediction and Reduction:

• Innovative 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 of 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 for subsonic engines anywhere from 10 to 20 EPNdB relative to FAR 36, Stage 3 certification levels.
• Highly accurate and efficient computational methods for the simulation of turbomachinery noise sources. Methods should have the potential of being 100 (or more) times faster than existing methods while accurately resolving acoustic disturbances.

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02.03 Subsonic Aircraft Systems Emissions Reduction

Current environmental concerns with subsonic 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 and NOx are both greenhouse gases, which impact the warming of the Earth's climate. Also, NOx 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, which appears as smog and causes breathing problems in humans. Current state-of-the-art engines and combustors in most subsonic aircraft are fuel efficient and meet the 1996 ICAO nitrogen oxide (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 ten years and by a factor of five within twenty years. Advanced concepts research for reducing CO2 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 subsonic aircraft operating conditions of interest include the landing-takeoff cycle as well as the in-flight portion of the mission.

Areas of particular interest include the following:

• New concepts for reducing carbon dioxide, oxides of nitrogen (NO, NO2, NOy), 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.
• New instrumentation techniques are needed for the measurement of engine emissions such as NOy, 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 2D and 3D data; time history measurements; and thin film, fiber optic, and MEMS-based sensors are of interest.

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