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  • 1
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    Cruise noise of an advanced propeller with swirl recovery vanes (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Keywords: ACOUSTICS
    Type: Journal of Aircraft (ISSN 0021-8669); 30; 2; p. 221-226.
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Cruise noise of the 2/9 scale model SR-7A propeller (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: ACOUSTICS
    Type: Journal of Aircraft (ISSN 0021-8669); 25; 740-746
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Potential reduction of en route noise from an advanced turboprop aircraft (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: When the en route noise of a representative aircraft powered by an eight-blade SR-7 propeller was previously calculated, the noise level was cited as a possible concern associated with the acceptance of advanced turboprop aircraft. Some potential methods for reducing the en route noise were then investigated and are reported. Source noise reductions from increasing the blade number and from operating at higher rotative speed to reach a local minimum noise point were investigated. Greater atmospheric attenuations for higher blade passing frequencies were also indicated. Potential en route noise reductions from these methods were calculated as 9.5 dB (6.5 dB(A)) for a 10-blade redesigned propeller and 15.5 dB (11 dB(A)) for a 12-blade redesigned propeller.
    Keywords: ACOUSTICS
    Type: NASA-TM-103635 , E-5809 , NAS 1.15:103635
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    The effect of front-to-rear propeller spacing on the interaction noise of a model counterrotation propeller at cruise conditions (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effect of front-to-rear propeller spacing on the interaction noise of a counterrotation propeller model was measured at cruise conditions. The data taken at an axial Mach number of 0.80 behaved as expected: interaction noise was reduced with increased spacing. The data taken at M=0.76 and M=0.72 did not behave as expected. At some of the test conditions the noise was unchanged; others even showed noise increases with increased spacing. A possible explanation, involving the amount of downstream blade area impacted by the tip vortex, is presented.
    Keywords: ACOUSTICS
    Type: NASA-TM-100121 , E-3667 , NAS 1.15:100121
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Cruise noise of the 2/9th scale model of the Large-scale Advanced Propfan (LAP) propeller, SR-7A (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Noise data on the Large-scale Advanced Propfan (LAP) propeller model SR-7A were taken in the NASA Lewis Research Center 8 x 6 foot Wind Tunnel. The maximum blade passing tone noise first rises with increasing helical tip Mach number to a peak level, then remains the same or decreases from its peak level when going to higher helical tip Mach numbers. This trend was observed for operation at both constant advance ratio and approximately equal thrust. This noise reduction or, leveling out at high helical tip Mach numbers, points to the use of higher propeller tip speeds as a possible method to limit airplane cabin noise while maintaining high flight speed and efficiency. Projections of the tunnel model data are made to the full scale LAP propeller mounted on the test bed aircraft and compared with predictions. The prediction method is found to be somewhat conservative in that it slightly overpredicts the projected model data at the peak.
    Keywords: ACOUSTICS
    Type: NASA-TM-100175 , E-3746 , NAS 1.15:100175
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Noise reduction for model counterrotation propeller at cruise by reducing aft-propeller diameter (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The forward propeller of a model counterrotation propeller was tested with its original aft propeller and with a reduced diameter aft propeller. Noise reductions with the reduced diameter aft propeller were measured at simulated cruise conditions. Reductions were as large as 7.5 dB for the aft-propeller passing tone and 15 dB in the harmonics at specific angles. The interaction tones, mostly the first, were reduced probably because the reduced-diameter aft-propeller blades no longer interacted with the forward propeller tip vortex. The total noise (sum of primary and interaction noise) at each harmonic was significantly reduced. The chief noise reduction at each harmonic came from reduced aft-propeller-alone noise, with the interaction tones contributing little to the totals at cruise. Total cruise noise reductions were as much as 3 dB at given angles for the blade passing tone and 10 dB for some of the harmonics. These reductions would measurably improve the fuselage interior noise levels and represent a definite cruise noise benefit from using a reduced diameter aft propeller.
    Keywords: ACOUSTICS
    Type: NASA-TM-88936 , E-3378 , NAS 1.15:88936
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Noise Trends of a 0.5 M (20 In.) Diameter Supersonic Throughflow Fan as Measured in an Unmodified Compressor Aerodynamic Test Facility (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The tone noise levels of a supersonic throughflow fan were measured at subsonic and supersonic axial duct Mach numbers. The noise in the inlet plenum showed no blade passing and harmonic tones at subsonic or supersonic axial flow conditions. At subsonic axial flow conditions, the supersonic throughflow fan showed no inlet plenum tones at fan operating conditions where tone noise had been previously measured for a subsonic fan design. This lower inlet-quadrant noise level for the supersonic throughflow fan was the result of high subsonic inlet velocities acting to reduce the noise propagating out the inlet. The fan noise, which was prevented from propagating upstream by the high subsonic inlet velocities, appeared to increase the noise in the exhaust duct at subsonic throughflow conditions. The exhaust duct noise decreased at supersonic axial throughflow Mach numbers, with the lowest blade passing and harmonic tones levels being observed at the design axial Mach number of 2.0. Multiple pure tone noise was observed in the inlet duct at subsonic axial flow Mach numbers but was seen only in the exhaust duct at supersonic axial flow conditions.
    Keywords: ACOUSTICS
    Type: NASA-TM-106041 , E-7618 , NAS 1.15:106041
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    An evaluation of some alternative approaches for reducing fan tone noise (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The potential of two alternative approaches for reducing fan ton noise was investigated in this study. One of these approaches increases the number of rotor blades to shift the tone noise to higher frequencies that are not rated as strongly by the perceived noise scale. This alternative fan also would have a small number of long chord stator vanes which would reduce the stator response and lower rotor-stator interaction noise. Comparison of the conventional and alternative fan concepts showed that this alternative approach has as large or larger a perceived tone noise reduction potential as the conventional approach. The other alternative, a high Mach number inlet, is evaluated both for its noise attenuation and for its change in noise directivity.
    Keywords: ACOUSTICS
    Type: NASA-TM-105356 , E-6730 , NAS 1.15:105356
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Detailed noise measurements on the SR-7A propeller: Tone behavior with helical tip Mach number (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Detailed noise measurements were taken on the SR-7A propeller to investigate the behavior of the noise with helical tip Mach number and then to level off as Mach number was increased further. This behavior was further investigated by obtaining detailed pressure-time histories of data. The pressure-time histories indicate that a portion of the primary pressure pulse is progressively cancelled by a secondary pulse which results in the noise leveling off as the helical tip Mach number is increased. This second pulse appears to originate on the same blade as the primary pulse and is in some way connected to the blade itself. This leaves open the possibility of redesigning the blade to improve the cancellation; thereby, the propeller noise is reduced.
    Keywords: ACOUSTICS
    Type: NASA-TM-105206 , E-6519 , NAS 1.15:105206
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    A concept for a counterrotating fan with reduced tone noise (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: As subsonic jet engine designs incorporate higher bypass ratios to reduce jet noise and increase engine cycle efficiency, the fan noise becomes a significant part of the perceived total noise. The conventional method of reducing fan tone noise is to design a low tip-speed device. An alternative approach of using a counterrotating fan with a high number of rotor blades is investigated in this report. The source of noise at the blade passing frequency of this device is the rotor-only mechanism, which is cut off for a subsonic tip speed rotor. The interaction noise occurs at twice the blade passing frequency, which, for this fan, was shifted high enough in frequency to be above the perceived noise rating range. The result was a counterrotating fan which had more potential for tone noise reduction than does the conventional fan. A potential broadband noise reduction was also indicated.
    Keywords: ACOUSTICS
    Type: NASA-TM-105736 , E-7138 , NAS 1.15:105736
    Format: application/pdf
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