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  • 1
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    Microwave backscattering from surf zone waves (2014)
    Wiley
    Details
    Publication Date: 2014-05-11
    Description: The microwave backscatter properties of surf zone waves are analysed using field observations. By utilizing a pre-existing, independent, water surface discrimination technique the microwave returns were extracted along individual wave forms and the data from shoaling (steepening) waves, surf zone breaking waves, and remnant foam were separated and quantified. In addition, a wave tracking analysis technique allows the returns to be examined on a wave-by-wave basis as individual waves progress through the shoaling zone and break on a nearshore sand bar. Normalized radar cross-sections (NRCS), polarization ratios, Doppler spectra, and scatterer velocities were collected using a dual-polarized, X-band radar operating at lower grazing angles than previously reported (1°-3.5°). The results indicate that the maximum NRCS levels are from the active breaking portions of the wave and were consistently about -20 dB, regardless of radar polarization, azimuth angle, wave height, or wind speed. In addition, breaking waves induce broadening of the Doppler spectra and mean scatterer velocities that correlate well with the carrier wave celerity. Analysis of the polarization ratios suggest that the active breaking portions of the wave are depolarized but that higher polarization ratios (〉0 dB) are found on the leading edges shoreward of the active breaking portions of the waves, which indicates a clear distinction between two scattering regimes. These results are consistent with scattering from a very rough surface that is being mechanically generated by the breaking process, showing a good agreement with the expected grazing angle dependency of a Lambertian scatterer.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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    PAPER CURRENT
  • 2
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    A NASA Lewis comparative propulsion system assessment for the High-Speed Civil Transport (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The topics covered include the following: High Speed Research (HSR) Propulsion System Studies; HRS System Study flowpath; design point aircraft sizing - no noise constraint; impact of noise constraint; noise impact on aircraft size; takeoff gross weight assessment; impact of High Speed Civil Transport (HSCT) high-altitude flyover noise; HSR NO(x) reduction status; current assessment of HSCT ozone depletion; influence of non-optimum cruise altitude on range; and influence of subsonic leg on range.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA. Langley Research Center, First Annual High-Speed Research Workshop, Part 2; p 831-865
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Comparison of turbine bypass and mixed flow turbofan engines for a high-speed civil transport (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A comparison of the turbine bypass engine and the mixed flow turbofan for a Mach 2.4 cruise application is presented. A parametric assessment is conducted for each cycle. Parameters that are investigated for the turbine bypass engine include design bypass, combustor exit temperature, and overall pressure ratio. Parameters that are investigated for the mixed flow turbofan include fan pressure ratio, mixer design pressure ratio, and combustor exit temperature. The engines are analyzed for a 5000-nautical-mile, all supersonic cruise mission to determine the aircraft takeoff gross weights. The effects of takeoff noise, cruise emissions, the addition of subsonic cruise legs, and constrained supersonic cruise altitudes are also evaluated.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-3132
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    A Noise and Emissions Assessment of the N3-X Transport (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Analytical predictions of certification noise and exhaust emissions for NASA's N3-X - a notional, hybrid wingbody airplane - are presented in this paper. The N3-X is a 300-passenger concept transport propelled by an array of fans distributed spanwise near the trailing edge of the wingbody. These fans are driven by electric motors deriving power from twin generators driven by turboshaft engines. Turboelectric distributed hybrid propulsion has the potential to dramatically increase the propulsive efficiency of aircraft. The noise and exhaust emission estimates presented here are generated using NASA's conceptual design systems analysis tools with several key modifications to accommodate this unconventional architecture. These tools predict certification noise and the emissions of oxides of nitrogen by leveraging data generated from a recent analysis of the N3-X propulsion system.
    Keywords: Aircraft Propulsion and Power; Aircraft Design, Testing and Performance
    Type: AIAA Paper 2014-0594 , E-18841-1 , AIAA SciTech; Jan 13, 2014 - Jan 17, 2014; National Harbor, MD; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Analysis of a Stretched Derivative Aircraft with Open Rotor Propulsion (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Research into advanced, high-speed civil turboprops received significant attention during the 1970s and 1980s when fuel efficiency was the driving focus of U.S. aeronautical research. But when fuel prices declined sharply there was no longer sufficient motivation to continue maturing the technology. Recent volatility in fuel prices and increasing concern for aviation's environmental impact, however, have renewed interest in unducted, open rotor propulsion and revived research by NASA and a number of engine manufacturers. Recently, NASA and General Electric have teamed to conduct several investigations into the performance and noise of an advanced, single-aisle transport with open rotor propulsion. The results of these initial studies indicate open rotor engines have the potential to provide significant reduction in fuel consumption compared to aircraft using turbofan engines with equivalent core technology. In addition, noise analysis of the concept indicates that an open rotor aircraft in the single-aisle transport class would be able to meet current noise regulations with margin. The behavior of derivative open rotor transports is of interest. Heavier, "stretched" derivative aircraft tend to be noisier than their lighter relatives. Of particular importance to the business case for the concept is how the noise margin changes relative to regulatory limits within a family of similar open rotor aircraft. The subject of this report is a performance and noise assessment of a notional, heavier, stretched derivative airplane equipped with throttle-push variants of NASA's initial open rotor engine design.
    Keywords: Aircraft Design, Testing and Performance; Aircraft Propulsion and Power
    Type: ISABE2015-22081 , GRC-E-DAA-TN21868 , International Symposium on Airbreathing Engines; Oct 25, 2015 - Oct 30, 2015; Phoenix, AZ; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Initial Assessment of Open Rotor Propulsion Applied to an Advanced Single-Aisle Aircraft (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Application of high speed, advanced turboprops, or propfans, to subsonic transport aircraft received significant attention and research in the 1970s and 1980s when fuel efficiency was the driving focus of aeronautical research. Recent volatility in fuel prices and concern for aviation s environmental impact have renewed interest in unducted, open rotor propulsion, and revived research by NASA and a number of engine manufacturers. Unfortunately, in the two decades that have passed since open rotor concepts were thoroughly investigated, NASA has lost experience and expertise in this technology area. This paper describes initial efforts to re-establish NASA s capability to assess aircraft designs with open rotor propulsion. Specifically, methodologies for aircraft-level sizing, performance analysis, and system-level noise analysis are described. Propulsion modeling techniques have been described in a previous paper. Initial results from application of these methods to an advanced single-aisle aircraft using open rotor engines based on historical blade designs are presented. These results indicate open rotor engines have the potential to provide large reductions in fuel consumption and emissions. Initial noise analysis indicates that current noise regulations can be met with old blade designs and modern, noiseoptimized blade designs are expected to result in even lower noise levels. Although an initial capability has been established and initial results obtained, additional development work is necessary to make NASA s open rotor system analysis capability on par with existing turbofan analysis capabilities.
    Keywords: Aircraft Design, Testing and Performance
    Type: NF1676L-12112 , 11th AIAA Aviation Technology, Integration, and Operations (ATIO) Conference; Sep 20, 2011 - Sep 22, 2011; Virginia Beach, VA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Updated Assessment of an Open Rotor Airplane Using an Advanced Blade Design (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Application of open rotor propulsion systems (historically referred to as "advanced turboprops" or "propfans") to subsonic transport aircraft received significant attention and research in the 1970s and 1980s when fuel efficiency was the driving focus of aeronautical research. Recent volatility in fuel prices and concern for aviation's environmental impact have renewed interest in open rotor propulsion, and revived research by NASA and a number of engine manufacturers. Over the last few years, NASA has revived and developed analysis capabilities to assess aircraft designs with open rotor propulsion systems. These efforts have been described in several previous papers along with initial results from applying these capabilities. The initial results indicated that open rotor engines have the potential to provide large reductions in fuel consumption and emissions. Initial noise analysis indicated that current noise regulations can be met with modern baseline blade designs. Improved blades incorporating low-noise features are expected to result in even lower noise levels. This paper describes improvements to the initial assessment, plus a follow-on study using a more advanced open rotor blade design to power the advanced singleaisle transport. The predicted performance and environmental results of these two advanced open rotor concepts are presented and compared.
    Keywords: Aircraft Propulsion and Power; Aircraft Design, Testing and Performance
    Type: NASA/TM-2013-218074 , E-18749 , AIAA Paper 2013-3628 , Joint Propulsion Conference and Exhibit; Jul 14, 2013 - Jul 17, 2013; San Jose, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    An N+3 Technology Level Reference Propulsion System (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: An N+3 technology level engine, suitable as a propulsion system for an advanced single-aisle transport, was developed as a reference cycle for use in technology assessment and decision-making efforts. This reference engine serves three main purposes: it provides thermodynamic quantities at each major engine station, it provides overall propulsion system performance data for vehicle designers to use in their analyses, and it can be used for comparison against other proposed N+3 technology-level propulsion systems on an equal basis. This reference cycle is meant to represent the expected capability of gas turbine engines in the N+3 timeframe given reasonable extrapolations of technology improvements and the ability to take full advantage of those improvements.
    Keywords: Aircraft Propulsion and Power; Aircraft Design, Testing and Performance
    Type: NASA/TM-2017-219501 , E-19373 , GRC-E-DAA-TN41487
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Performance and Environmental Assessment of an Advanced Aircraft with Open Rotor Propulsion (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Application of high speed, advanced turboprops, or "propfans," to transonic transport aircraft received significant attention during the 1970s and 1980s when fuel efficiency was the driving focus of aeronautical research. Unfortunately, after fuel prices declined sharply there was no longer sufficient motivation to continue maturing this technology. Recent volatility in fuel prices and increasing concern for aviation s environmental impact, however, have renewed interest in unducted, open rotor propulsion. Because of the renewed interest in open rotor propulsion, the lack of publicly available up-to-date studies assessing its benefits, and NASA s focus on reducing fuel consumption, a preliminary aircraft system level study on open rotor propulsion was initiated to inform decisions concerning research in this area. New analysis processes were established to assess the characteristics of open rotor aircraft. These processes were then used to assess the performance, noise, and emissions characteristics of an advanced, single-aisle aircraft using open rotor propulsion. The results of this initial study indicate open rotor engines have the potential to provide significant reductions in fuel consumption and landing-takeoff cycle NOX emissions. Noise analysis of the study configuration indicates that an open rotor aircraft in the single-aisle class would be able to meet current noise regulations with margin.
    Keywords: Aeronautics (General)
    Type: NASA/TM-2012-217772 , L-20189 , NF1676L-15385
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    A Subsonic Aircraft Design Optimization With Neural Network and Regression Approximators (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Flight-Optimization-System (FLOPS) code encountered difficulty in analyzing a subsonic aircraft. The limitation made the design optimization problematic. The deficiencies have been alleviated through use of neural network and regression approximations. The insight gained from using the approximators is discussed in this paper. The FLOPS code is reviewed. Analysis models are developed and validated for each approximator. The regression method appears to hug the data points, while the neural network approximation follows a mean path. For an analysis cycle, the approximate model required milliseconds of central processing unit (CPU) time versus seconds by the FLOPS code. Performance of the approximators was satisfactory for aircraft analysis. A design optimization capability has been created by coupling the derived analyzers to the optimization test bed CometBoards. The approximators were efficient reanalysis tools in the aircraft design optimization. Instability encountered in the FLOPS analyzer was eliminated. The convergence characteristics were improved for the design optimization. The CPU time required to calculate the optimum solution, measured in hours with the FLOPS code was reduced to minutes with the neural network approximation and to seconds with the regression method. Generation of the approximators required the manipulation of a very large quantity of data. Design sensitivity with respect to the bounds of aircraft constraints is easily generated.
    Keywords: Aircraft Design, Testing and Performance
    Type: NASA/TM-2004-213059 , AIAA Paper 2004-4606 , E-14504 , 10th Multidisciplinary Analysis and Optimization Conference; Aug 30, 2004 - Sep 01, 2004; Albany, NY; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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