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  • Acoustics  (9)
  • Geophysics  (6)
  • 2005-2009  (8)
  • 1995-1999  (7)
  • 1
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    Influence of Shock-Induced Ionospheric Conductivity Enhancements on Storm Main Phase Intensities (1999)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: International Union of Geodesy and Geophysics (IUGG) '99; Birmingham; United Kingdom
    Format: text
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  • 2
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    Interball substorm observations: Christmas for space scientists (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Observational results from the Interball Tail Probe spacecraft are presented. One of the main objectives of the Interball project is to study the dynamic processes in the magnetosphere. Three events observed by the spacecraft's instruments are investigated: a pseudobreakup during which earthward streaming ions were observed in the vicinity of a thin current sheet; a substorm in which the magnetic signatures in the lobe and on the ground were preceeded by northward re-orientation of the interplanetary magnetic field Bz component; and a magnetic storm at the beginning of which extreme deformation of the magnetotail was observed.
    Keywords: Geophysics
    Type: ; 497-506
    Format: text
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  • 3
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    Turbofan Noise Reduction Associated With Increased Bypass Nozzle Flow (2005)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: An advanced 22-in. scale model turbofan, typical of a current-generation aircraft engine design by GE Aircraft Engines, was tested in NASA Glenn Research Center s 9- by 15- Foot Low-Speed Wind Tunnel to explore the far-field acoustic effects of an increased bypass nozzle area at simulated aircraft speeds of takeoff, approach, and landing. The wind-tunnel-scale model consisted of the bypass stage fan, stators, and nacelle (including the fan exit nozzle) of a typical turbofan. This fan-stage test was part of the NASA Glenn Fan Broadband Source Diagnostic Test, second entry, which acquired aeroacoustic results over a range of test conditions. A baseline nozzle was selected, and the nozzle area was chosen for maximum performance at sea-level conditions. Two additional nozzles were also tested--one with a 5.4-percent increase in nozzle area over the baseline nozzle (sized for design point conditions), corresponding to a 5-percent increase in fan weight flow, and another nozzle with a 10.9-percent increase in nozzle area over the baseline nozzle (sized for maximum weight flow at sea-level conditions), corresponding to a 7.5 percent increase in fan weight flow. Measured acoustic benefits with increased nozzle area were very encouraging, showing overall sound power level reductions of 2 dB or more (left graph) while the stage adiabatic efficiency (right graph) and thrust (final graph) actually increased by several percentage points. These noise-reduction benefits were seen to include both rotor-interaction tones and broadband noise, and were evident throughout the range of measured sideline angles.
    Keywords: Acoustics
    Type: Research and Technology 2004; NASA/TM-2005-213419
    Format: application/pdf
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  • 4
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    Derivation of Acoustic Criteria for the Cassini Spacecraft and Comparison with Flight Data (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Acoustic measurements from eight pre-Cassini Titan IV flights, and an acoustic test of a Cassini simulator and Titan payload fairing (PLF), were used to derive acoustic flight and test criteria for the Cassini spacecraft. The flight and ground test data were used or modified to account for the following factors: (a) noise-spike contamination of flight data, (b) spatial and flight-to-flight variations of flight data, (c) application of a thicker banier-blanket to the PLF for the Cassini mission, (d) effects of locating two Cassini assemblies, the Huygens Probe, and the High Gain Antenna (HGA), near the PLF, and (e) higher thrust of upgraded Titan solid rocket motors (SRMS) for the Cassini mission. An overall sound pressure level (OA SPL) of 145 dB was verified for the protoflight acoustic test criteria for the Cassini spacecraft. Cassini flight liftoff data showed an average OA SPL of 133 dB.
    Keywords: Acoustics
    Type: International Congress on Sound and Vibration; Jul 05, 1999 - Jul 08, 1999; Lyngby; Denmark
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  • 5
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    Benefits of Swept and Leaned Stators for Fan Noise Reduction (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An advanced high bypass ratio fan model was tested in the NASA Lewis Research Center 9 x 15-Foot Low Speed Wind Tunnel. The primary focus of this test was to quantify the acoustic benefits and aerodynamic performance of sweep and lean in stator vane design. Three stator sets were used for this test series. A conventional radial stator was tested at two rotor-stator axial spacings. Additional stator sets incorporating sweep + lean, and sweep only were also tested. The hub axial location for the swept + lean, and sweep only stators corresponded to the location of the radial stator at the upstream rotor-stator spacing, while the tip axial location of these modified stators corresponded to the radial stator axial position at the downstream position. The acoustic results show significant reductions in both rotor-stator interaction noise and broadband noise beyond what could be achieved through increased axial spacing of the conventional, radial stator. Theoretical application of these results to acoustically quantify a fictitious 2-engine aircraft and flight path suggested that about 3 Effective Perceived Noise (EPN) dB could be achieved through incorporation of these modified stators. This reduction would represent a significant portion of the 6 EPNdB noise goal of the current NASA Advanced Subsonic Technology (AST) initiative relative to that of 1992 technology levels. A secondary result of this fan test was to demonstrate the ability of an acoustic barrier wall to block aft-radiated fan noise in the wind tunnel, thus revealing the acoustic structure of the residual inlet-radiated noise. This technology should prove valuable toward better understanding inlet liner design, or wherever it is desirable to eliminate aft-radiated noise from the fan acoustic signature.
    Keywords: Acoustics
    Type: NASA/TM-1998-208661 , NAS 1.15:208661 , AIAA Paper 99-0479 , E-11382 , Aerospace Sciences Meeting and Exhibit; Jan 11, 1999 - Jan 14, 1999; Reno, NV; United States
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  • 6
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    A Statistical Study of the Global Structure of the Ring Current (1997)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: In this paper we derive the average configuration of the ring current as a function of the state of the magnetosphere as indicated by the Dst index. We sort magnetic field data from the Combined Release and Radiation Effects Satellite (CRRES) by spatial location and by the Dst index in order to produce magnetic field maps. From these maps we calculate local current systems by taking the curl of the magnetic field. NN7e find both the westward (outer) and the eastward (inner) components of the ring current. We find that the ring current intensity varies linearly with D.St as expected, and that the ring current is asymmetric for all Dst values. The azimuthal peak of the ring current is located in the afternoon sector for quiet conditions, and near midnight for disturbed conditions. The ring current also moves closer to the Earth during disturbed conditions. We are able to recreate the Dst index by integrating the magnetic perturbations caused by the ring current. We find that we needed to apply a 20 nT offset to Dst, and assume a perfectly conducting Earth to obtain an optimal agreement between the computed and the observed Dst. We interpret the 20 nT offset as the magnetic field generated by the quiet time ring current used as baseline in computing Dst.
    Keywords: Geophysics
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  • 7
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    Vibroacoustic Analysis of Large Heat Rejection Radiators for Future Spacecraft (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Spacecraft structures such as antennas, solar arrays and radiator panels significantly respond to high acoustic levels seen at lift-off. Some future spacecraft may utilize nuclear electric propulsion that require large radiator panels to reject waste heat. A vibroacoustic assessment was performed for two different radiator panel designs. Results from the analysis of the two designs using different analytical approaches are presented and discussed.
    Keywords: Acoustics
    Type: Spacecraft and Launch Vehicle Dynamic Environment Workshop; Jun 21, 2005 - Jun 23, 2005; El Segundo, CA; United States
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  • 8
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    Ultra High Bypass Ratio Engine Research for Reducing Noise, Emissions, and Fuel Consumption (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A pictorial history of NASA development of advanced engine technologies for reducing environmental emissions and increasing performance from the 1970s to 2000s is presented. The goals of the Subsonic Fixed Wing Program portion of the NASA Fundamental Aeronautics Program are discussed, along with the areas of investigation currently being pursued by the Ultra High Bypass Partnership Element of the Subsonic Fixed Wing Program.
    Keywords: Acoustics
    Type: Fundamental Aeronautics 2007 Annual Meeting; Oct 30, 2007 - Nov 01, 2007; New Orleans, LA; United States
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  • 9
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    Assessment of Soft Vane and Metal Foam Engine Noise Reduction Concepts (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Two innovative fan-noise reduction concepts developed by NASA are presented - soft vanes and over-the-rotor metal foam liners. Design methodologies are described for each concept. Soft vanes are outlet guide vanes with internal, resonant chambers that communicate with the exterior aeroacoustic environment via a porous surface. They provide acoustic absorption via viscous losses generated by interaction of unsteady flows with the internal solid structure. Over-the-rotor metal foam liners installed at or near the fan rotor axial plane provide rotor noise absorption. Both concepts also provide pressure-release surfaces that potentially inhibit noise generation. Several configurations for both concepts are evaluated with a normal incidence tube, and the results are used to guide designs for implementation in two NASA fan rigs. For soft vanes, approximately 1 to 2 dB of broadband inlet and aft-radiated fan noise reduction is achieved. For over-the-rotor metal foam liners, up to 3 dB of fan noise reduction is measured in the low-speed fan rig, but minimal reduction is measured in the high-speed fan rig. These metal foam liner results are compared with a static engine test, in which inlet sound power level reductions up to 5 dB were measured. Brief plans for further development are also provided.
    Keywords: Acoustics
    Type: AIAA Paper 2009-3142 , LF99-8002 , 15th AIAA/CEAS Aeroacoustics Conference; May 11, 2009 - May 13, 2009; Miami, FL; United States
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  • 10
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    Role of Coronal Mass Ejections in the Heliospheric Hale Cycle (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The 11-year solar cycle variation in the heliospheric magnetic field strength can be explained by the temporary buildup of closed flux released by coronal mass ejections (CMEs). If this explanation is correct, and the total open magnetic flux is conserved, then the interplanetary-CME closed flux must eventually open via reconnection with open flux close to the Sun. In this case each CME will move the reconnected open flux by at least the CME footpoint separation distance. Since the polarity of CME footpoints tends to follow a pattern similar to the Hale cycle of sunspot polarity, repeated CME eruption and subsequent reconnection will naturally result in latitudinal transport of open solar flux. We demonstrate how this process can reverse the coronal and heliospheric fields, and we calculate that the amount of flux involved is sufficient to accomplish the reversal within the 11 years of the solar cycle.
    Keywords: Geophysics
    Type: Geophysical Research Letters (ISSN 0094-8276); 34
    Format: text
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