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  • 1
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    Structureborne noise control in advanced turboprop aircraft (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Structureborne noise is discussed as a contributor to propeller aircraft interior noise levels that are nonresponsive to the application of a generous amount of cabin sidewall acoustic treatment. High structureborne noise levels may jeopardize passenger acceptance of the fuel-efficient high-speed propeller transport aircraft designed for cruise at Mach 0.65 to 0.85. These single-rotation tractor and counter-rotation tractor and pusher propulsion systems will consume 15 to 30 percent less fuel than advanced turbofan systems. Structureborne noise detection methodologies and the importance of development of a structureborne noise sensor are discussed. A structureborne noise generation mechanism is described in which the periodic components or propeller swirl produce periodic torques and forces on downstream wings and airfoils that are propagated to the cabin interior as noise. Three concepts for controlling structureborne noise are presented: (1) a stator row swirl remover, (2) selection of a proper combination of blade numbers in the rotor/stator system of a single-rotation propeller, and the rotor/rotor system of a counter-rotation propeller, and (3) a tuned mechanical absorber.
    Keywords: ACOUSTICS
    Type: NASA-TM-88947 , E-3362 , NAS 1.15:88947 , AIAA PAPER 87-0530
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    In-flight near- and far-field acoustic data measured on the Propfan Test Assessment (PTA) testbed and with an adjacent aircraft (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Flight tests to define the far-field tone source at cruise conditions were completed on the full-scale SR-7L advanced turboprop that was installed on the left wing of a Gulfstream 2 aircraft. This program, designated Propfan Test Assessment (PTA), involved aeroacoustic testing of the propeller over a range of test conditions. These measurements defined source levels for input into long-distance propagation models to predict en route noise. In-flight data were taken for seven test cases. Near-field acoustic data were taken on the Gulfstream fuselage and on a microphone boom that was mounted on the Gulfstream wing outboard of the propeller. Far-field acoustic data were taken by an acoustically instrumented Learjet that flew in formation with the Gulfstream. These flight tests were flown from El Paso, Texas, and from the NASA Lewis Research Center. A comprehensive listing of the aeroacoustic results from these flight tests which may be used for future analysis are presented.
    Keywords: ACOUSTICS
    Type: NASA-TM-103719 , E-6402 , NAS 1.15:103719
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Measured far-field flight noise of a counterrotation turboprop at cruise conditions (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Modern high speed propeller (advanced turboprop) aircraft are expected to operate on 50 to 60 percent less fuel than the 1980 vintage turbofan fleet while at the same time matching the flight speed and performance of those aircraft. Counterrotation turboprop engines offer additional fuel savings by means of upstream propeller swirl recovery. This paper presents acoustic sideline results for a full-scale counterrotation turboprop engine at cruise conditions. The engine was installed on a Boeing 727 aircraft in place of the right-side turbofan engine. Acoustic data were taken from an instrumented Learjet chase plane. Sideline acoustic results are presented for 0.50 and 0.72 Mach cruise conditions. A scale model of the engine propeller was tested in a wind tunnel at 0.72 Mach cruise conditions. The model data were adjusted to flight acquisition conditions and were in general agreement with the flight results.
    Keywords: ACOUSTICS
    Type: NASA-TM-101383 , E-4437 , NAS 1.15:101383
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Structureborne noise control in advanced turboprop aircraft (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Structureborne noise is discussed as a contributor to propeller aircraft interior noise levels that are nonresponsive to the application of a generous amount of cabin sidewall acoustic treatment. High structureborne noise levels may jeopardize passenger acceptance of the fuel-efficient high-speed propeller transport aircraft designed for cruise at Mach 0.65 to 0.85. These single-rotation tractor and counter-rotation tractor and pusher propulsion systems will consume 15 to 30 percent less fuel than advanced turbofan systems. Structureborne noise detection methodologies and the importance of development of a structureborne noise sensor are discussed. A structureborne noise generation mechanism is described in which the periodic components or propeller swirl produce periodic torques and forces on downstream wings and airfoils that are propagated to the cabin interior as noise. Three concepts for controlling structureborne noise are presented: (1) a stator row swirl remover, (2) selection of a proper combination of blade numbers in the rotor/stator system of a single-rotation propeller, and the rotor/rotor system of a counter-rotation propeller, and (3) a tuned mechanical absorber.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 87-0530
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Sputtering from a Porous Material by Penetrating Ions (2012)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Porous materials are ubiquitous in the universe and weathering of porous surfaces plays an important role in the evolution of planetary and interstellar materials. Sputtering of porous solids in particular can influence atmosphere formation, surface reflectivity, and the production of the ambient gas around materials in space, Several previous studies and models have shown a large reduction in the sputtering of a porous solid compared to the sputtering of the non-porous solid. Using molecular dynamics simulations we study the sputtering of a nanoporous solid with 55% of the solid density. We calculate the electronic sputtering induced by a fast, penetrating ion, using a thermal spike representation of the deposited energy. We find that sputtering for this porous solid is, surprisingly, the same as that for a full-density solid, even though the sticking coefficient is high.
    Keywords: Space Sciences (General)
    Type: GSFC.JA.7459.2012 , The Astrophysical Journal Letters; 743; 1; L5
    Format: text
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  • 6
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    Radiation-Induced Amorphization of Crystalline Ice (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We study radiation-induced amorphization of crystalline ice, ana lyzing the resu lts of three decades of experiments with a variety of projectiles, irradiation energy, and ice temperature, finding a similar trend of increasing resistance of amorphization with temperature and inconsistencies in results from different laboratories. We discuss the temperature dependence of amorphization in terms of the 'thermal spike' model. We then discuss the common use of the 1.65 micrometer infrared absorption band of water as a measure of degree of crystallinity, an increasingly common procedure to analyze remote sensing data of astronomical icy bodies. The discussion is based on new, high quality near-infrared refl ectance absorption spectra measured between 1.4 and 2.2 micrometers for amorphous and crystalline ices irradiated with 225 keV protons at 80 K. We found that, after irradiation with 10(exp 15) protons per square centimeter, crystalline ice films thinner than the ion range become fully amorphous, and that the infrared absorption spectra show no significant changes upon further irradiation. The complete amorphization suggests that crystalline ice observed in the outer Solar System, including trans-neptunian objects, may results from heat from internal sources or from the impact of icy meteorites or comets.
    Keywords: Astrophysics
    Type: GSFC.JA.4461.2011 , Icarus (ISSN 0019-1035); 207; 1; 314-319
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    NASA TECHNICAL REPORTS
  • 7
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    Farfield inflight measurement of high-speed turboprop noise (1982)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A flight program was carried out to determine the variation of noise level with distance from a model high speed propeller. Noise measurements were obtained at different distances from a SR-3 propeller mounted on a JetStar aircraft, with the test instrumentation mounted on a Lear jet flown in formation. The propeller was operated at 0.8 flight Mach number, 1.12 helical tip Mach number and at 0.7 flight Mach number, 1.0 helical tip Mach number. The instantaneous pressure from individual blades was observed to rise faster at the 0.8 M flight speed, than at the 0.7 M flight speed. The measured levels appeared to decrease in good agreement with a 6 dB/doubling of distance decay, over the measurement range of approximately 16 m to 100 m distance. Further extrapolation, to the distances represented by a community, would suggest that the propagated levels during cruise would not cause a serious community annoyance.
    Keywords: ACOUSTICS
    Type: NASA-TM-83327 , E-1574 , NAS 1.15:83327 , AIAA PAPER 83-9745 , AIAA 8th Aeroacoustics Conf.; Apr 11, 1983 - Apr 13, 1983; Atlanta
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Understanding the Space Weathering of Mercury via Simulation of Micrometeorite Impacts (2019)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Space weathering alters the surfaces of airless planetary bodies via irradiation from the solar wind and micrometeorite impacts. These processes modify the microstructure, chemical composition, and spectral properties of surface materials, typically resulting in the reddening (increasing reflectance with increasing wavelength), darkening (reducing albedo), and attenuation of characteristic absorption features in reflectance spectra. In lunar samples, these changes in optical properties are driven by the production of reduced nanophase Fe particles (npFe). Our understanding of space weathering has largely been based on data from the Moon and, more recently, near-Earth S-type asteroids. However, the environment at Mercury is significantly different, with the surface experiencing intense solar wind irradiation and higher velocity micrometeorite impacts. Additionally, the composition of Mercurys surface varies significantly from that of the Moon, including a component with very low albedo known as low reflectance material (LRM) which is enriched with up to 4 wt.% carbon over the local mean. Our understanding of how carbon phases, including graphite, are altered as a result of these processes is limited.
    Keywords: Space Sciences (General)
    Type: JSC-E-DAA-TN64971 , Lunar and Planetary Science Conference; Mar 18, 2019 - Mar 22, 2019; Woodlands, TX; United States
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  • 9
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    Radiolysis and Photolysis of Icy Satellite Surfaces: Experiments and Theory (2010)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The transport and exchange of material between bodies in the outer solar system is often facilitated by their exposure to ionizing radiation. With this in mind we review the effects of energetic ions, electrons and UV photons on materials present in the outer solar system. We consider radiolysis, photolysis, and sputtering of low temperature solids. Radiolysis and photolysis are the chemistry that follows the bond breaking and ionization produced by incident radiation, producing, e.g., O2 and H2 from irradiated H2O ice. Sputtering is the ejection of molecules by incident radiation. Both processes are particularly effective on ices in the outer solar system. Materials reviewed include H2O ice, sulfur-containing compounds (such as S02 and S8), carbon~contajning compounds (such as CH4), nitrogen-containing compounds (such as NH3 and N2), and mixtures of those compounds. We also review the effects of ionizing radiation on a mixture of N2 and CH4 gases, as appropriate to Titan's upper atmosphere, where radiolysis and photolysis produce complex organic compounds (tholins).
    Keywords: Astrophysics
    Type: GSFC.JA.4460.2011 , Space Science Reviews; 153; 4-Jan; 299-315
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    NASA TECHNICAL REPORTS
  • 10
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    A Model Study of the Thermal Evolution of Astrophysical Ices (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We address the question of the evolution of ices that have been exposed to radiation from stellar sources and cosmic rays. We studied in the laboratory the thermal evolution of a model ice sample: a mixture of water, hydrogen peroxide, dioxygen, and ozone produced by irradiating solid H2O2 with 50 keV H(+) at 17 K. The changes in composition and release of volatiles during warming to 200 K were monitored by infrared spectroscopy, mass spectrometry, and microbalance techniques. We find evidence for voids in the water component from the infrared bands due to dangling H bonds. The absorption from these bands increases during heating and can be observed at temperatures as high as approx. 155 K. More O2 is stored in the radiolyzed film than can be retained by codeposition of O2 and H2O. This O2 remains trapped until approx. 155 K, where it desorbs in an outburst as water ice crystallizes. Warming of the ice also drastically decreases the intrinsic absorbance of O2 by annealing defects in the ice. We also observe loss of O3 in two stages during heating, which correlates with desorption and possibly chemical reactions with radicals stored in the ice, triggered by the temperature increase.
    Keywords: Astrophysics
    Type: The Astrophysical Journal; 639; L103-L106
    Format: text
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