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  • 1
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    Model ducted propulsor noise characteristics at takeoff conditions (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A model Advanced Ducted Propulsor (ADP) was tested in the NASA Lewis Low-Speed Anechoic Wind Tunnel at a simulated takeoff velocity of Mach 0.2. The model was designed and manufactured by Pratt & Whitney. The 16-blade rotor ADP was tested with 22- and 40-vane stators to achieve cut-on and cut-off criterion with respect to propagation of the fundamental rotor-stator interaction tone. Additional test parameters included three inlet lengths, three nozzle sizes, two spinner configurations, and two rotor rub strip configurations. The model was tested over a range of rotor blade setting angles and inlet angles of attack. Acoustic data were taken with a sideline translating microphone probe and with a unique inlet microphone probe that identified inlet rotating acoustic modes. The beneficial acoustic effects of cut-off were clearly demonstrated. A 10-dB fundamental tone reduction was associated with the long inlet and 40-vane stator. The fundamental tone level was essentially unaffected by inlet angle of attack at rotor speeds of above 96% design.
    Keywords: ACOUSTICS
    Type: Journal of Aircraft (ISSN 0021-8669); 31; 5; p. 1064-1070
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    New Fan Engine Noise-Reduction Concept Using Trailing Edge Blowing of Fan Blades Demonstrated (2002)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: A major source of noise in commercial turbofan engines is the interaction of the fan blade wakes with the fan exit vanes (stators). These wakes can be greatly reduced by filling them with air blown out of the blade trailing edge. Extensive testing of this concept has demonstrated significant noise reductions. These tests were conducted on a low-speed, 4- ft-diameter fan using hollow blades at NASA Glenn Research Center's Aeroacoustic Propulsion Laboratory (AAPL).
    Keywords: Acoustics
    Type: Research and Technology 2001; NASA/TM-2002-211333
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Far-field noise and internal modes from a ducted propeller at simulated aircraft takeoff conditions (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The ducted propeller offers structural and acoustic benefits typical of conventional turbofan engines while retaining much of the aeroacoustic benefits of the unducted propeller. A model Advanced Ducted Propeller (ADP) was tested in the NASA Lewis Low-Speed Anechoic Wind Tunnel at a simulated takeoff velocity of Mach 0.2. The ADP model was designed and manufactured by the Pratt and Whitney Division of United Technologies. The 16-blade rotor ADP was tested with 22- and 40-vane stators to achieve cut-on and cut-off criterion with respect to propagation of the fundamental rotor-stator interaction tone. Additional test parameters included three inlet lengths, three nozzle sizes, two spinner configurations, and two rotor rub strip configurations. The model was tested over a range of rotor blade setting angles and propeller axis angles-of-attack. Acoustic data were taken with a sideline translating microphone probe and with a unique inlet microphone probe which identified inlet rotating acoustic modes. The beneficial acoustic effects of cut-off were clearly demonstrated. A 5 dB fundamental tone reduction was associated with the long inlet and 40-vane sector, which may relate to inlet propeller axis angle-of-attack at rotor speeds of at least 96 percent design.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 92-0371
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Acoustic evaluation of the Helmholtz resonator treatment in the NASA Lewis 8- by 6-foot supersonic wind tunnel (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The acoustic consequences of sealing the Helmholtz resonators of the NASA Lewis 8- by 6-Foot Supersonic Wind Tunnel (8x6 SWT) were experimentally evaluated. This resonator sealing was proposed in order to avoid entrapment of hydrogen during tests of advanced hydrogen-fueled engines. The resonators were designed to absorb energy in the 4- to 20-Hz range; thus, this investigation is primarily concerned with infrasound. Limited internal and external noise measurements were made at tunnel Mach numbers ranging from 0.5 to 2.0. Although the resonators were part of the acoustic treatment installed because of a community noise problem their sealing did not seem to indicate a reoccurrence of the problem would result. Two factors were key to this conclusion: (1) A large bulk treatment muffler downstream of the resonators was able to make up for much of the attenuation originally provided by the resonators, and (2) there was no noise source in the tunnel test section. The previous community noise problem occurred when a large ramjet was tested in an open-loop tunnel configuration. If a propulsion system producing high noise levels at frequencies of less than 10 Hz were tested, the conclusion on community noise would have to be reevaluated.
    Keywords: ACOUSTICS
    Type: NASA-TM-101407 , E-4147 , NAS 1.15:101407
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Advanced turboprop wing installation effects measured by unsteady blade pressure and noise (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A single rotation model propeller (SR-7A) was tested at simulated takeoff/approach conditions (Mach 0.2), in the NASA Lewis 9- by 15-Ft Anechoic Wind Tunnel. Both unsteady blade surface pressures and noise measurements were made for a tractor configuration with propeller/straight wing and propeller alone configurations. The angle between the wing chord and propeller axis (droop angle) was varied along with the wing angle of attack to determine the effects on noise and unsteady loading. A method was developed that uses unsteady blade pressure measurements to provide a quantitative indication of propeller inflow conditions, at least for a uniform (across the propeller disk) inflow angle. The wing installation caused a nearly uniform upwash at the propeller inlet as evidenced by the domination of the pressure spectra by the first shaft order. This inflow angle increased at a rate of almost 150 percent of that of the wing angle-of-attack for a propeller-wing spacing of 0.54 wing chords at a constant droop angle. The flyover noise, as measured by the maximum blade passing frequency level, correlates closely with the propeller inflow angle (approx. 0.6 dB per degree of inflow angle) for all droop angles and wing angles of attack tested, including the propeller alone data. Large changes in the unsteady pressure responses on the suction surface of the blade were observed as the advance ratio was varied. The presence of a leading edge vortex may explain this behavior since changes in the location of this vortex would change with loading (advance ratio).
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-2719
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Fan Noise Source Diagnostic Test: Tone Modal Structure Results (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This investigation is part of a test series that was extremely comprehensive and included aerodynamic and acoustic testing of a fan stage using two different fan rotors and three different stator designs. The test series is known as the Source Diagnostic Test (SDT) and was conducted by NASA Glenn as part of the Advanced Subsonic Technology (AST) Noise Reduction Program. Tone mode measurements of one of the rotors with three different stators were made. The stator designs involve changes in vane count and sweep at constant solidity. The results of both inlet and exhaust tone mode measurements are presented in terms of mode power for both circumferential and radial mode orders. The results show benefits of vane sweep to be large, up to 13 dB in total tone power. At many conditions, the increase in power due to cutting on the rotor/stator interaction is more than offset by vane sweep. The rotor locked mode is shown as an important contributor to tone power when the blade tip speed is near and above Mach one. This is most evident in the inlet when the direct rotor field starts to cut on.
    Keywords: Aeronautics (General)
    Type: NASA/TM-2002-211594 , NAS 1.15:211594 , E-13378 , AIAA Paper 2002-2428 , Eighth Aeroacoustics Conference; Jun 17, 2002 - Jun 19, 2002; Breckenridge, CO; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Unsteady blade pressure measurements on a model counterrotation propeller (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: In an exploratory effort an advanced counterrotation propeller instrumented with blade-mounted pressure transducers was tested in the NASA Lewis 9- by 15-Foot Anechoic Wind Tunnel at a simulated takeoff and landing speed of Mach 0.20. The propeller's aft diameter was reduced to investigate possible noise reductions resulting from reduced blade row interaction with the tip vortex. The propeller was tested at three blade row spacings at fixed blade setting angles, at the maximum blade row spacing at higher blade setting angles and at propeller axis angles attack to the flow up to + or - 16 deg. A limited number of unsteady blade surface pressure measurements were made on both rotors of the model counterrotation propeller. Emphasis was placed on determining the effects of rotor-rotor interactions on the blade surface pressures. A unique method of processing the pressure signals was developed that enables even weak interaction waveforms and spectra to be separated from the total signal. The interaction on the aft rotor was many times stronger than that on the forward rotor. The fundamental rotor interaction tone exhibited complicated behavior but generally increased with rotational speed and blade setting angle and decreased with rotor spacing. With the propeller axis at an angle to the flow, the phase response of the aft rotor appeared to be significantly affected by the presence of the forward rotor.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 89-1144
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Low-noise fan exit guide vanes (2008)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Low-noise fan exit guide vanes are disclosed. According to the present invention a fan exit guide vane has an outer shell substantially shaped as an airfoil and defining an interior cavity. A porous portion of the outer shell allows communication between the fluctuations in the air passing over the guide vane and the interior cavity. At least one acoustically resonant chamber is located within the interior cavity. The resonant chamber is in communication with the porous portion of the outer perimeter. The resonant chamber is configured to reduce the noise generated at a predetermined frequency. In various preferred embodiments, there is a plurality of acoustically resonant chambers located within the interior cavity. The resonant chambers can be separated by one or more partitions within the interior cavity. In these embodiments, the resonant chambers can be configured to reduce the noise generated over a range of predetermined frequencies.
    Keywords: Aircraft Propulsion and Power
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Comparison of Tone Mode Measurements for a Forward Swept and Baseline Rotor Fan (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A forward swept fan, designated the Quite High Speed Fan (QHSF), was tested in the NASA Glenn 9- by 15-foot Low Speed Wind Tunnel to investigate its noise reduction relative to a baseline fan of the same aerodynamic performance. The design objective of the QHSF was a 6 dB reduction in Effective Perceived Noise Level relative to the baseline fan at the takeoff condition. The design noise reduction was to be a result of lower levels of multiple pure tone noise due to the forward swept rotor, and lower rotor/stator interaction tone noise from a leaned stator. Although the design 6 dB reduction was observed in far-field measurements, the induct mode measurements revealed the reasons for goals. All of the noise reduction was from the blade passing tone and its harmonics and most of this was unexpectedly from rotor/strut interaction modes. The reason for large differences in rotor/strut noise sources could not be determined with certainty. The reductions in the multiple pure tone noise for the forward swept rotor were not observed. this reduction were not the ones related to the design
    Keywords: Aeronautics (General)
    Type: NASA/TM-2003-212378 , E-13953 , NAS 1.15:212378 , AIAA Paper 2003-3293 , Ninth Aeroacoustics Conference and Exhibit; May 12, 2003 - May 14, 2003; Hilton Head, SC; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Duct Mode Measurements on the TFE731-60 Full Scale Engine (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A continuously rotating rake with radial microphones was developed to measure the inlet and exhaust duct modes on a TFE731-60 turbofan engine. This was the first time the rotating rake technology was used on a production engine. The modal signature for the first three fan harmonics was obtained in the inlet and exhaust. Rotor-stator and rotor-strut interaction modes were measured. Total harmonic power was calculated over a range of fan speeds. Above sonic tip speed, the rotor locked mode was not strong enough to be identified, but the 'buzz-saw' noise at fan sub-harmonics was identified.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2002-211573 , NAS 1.15:211573 , E-13310 , Eighth Aeroacoustics Conference; Jun 17, 2002 - Jun 19, 2002; Breckenridge, CO; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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