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  • 1
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    The theoretical and experimental investigations on multiple pure tone noise, part 1 (1971)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A theoretical and experimental investigation is described on multiple pure tone noise. Based on a two-dimensional and inviscid flow model, an analysis is developed to predict the generation and subsequent evolution of multiple pure tone noise from prescribed blade-to-blade nonuniformities in the rotor geometry. The results show that even small nonuniformities within manufacturing tolerances can cause a significant amount of multiple pure tone noise. Among the different kinds of nonuniformities investigated, errors in blade spacings are a weaker generator of multiple pure tone noise than errors in blade stagger or blade contours. Experimental investigations of the effects of the rotor relative Mach number, incidence angle and length of the inlet duct on the evolution of the multiple pure tone noise are conducted with a known distribution of rotor nonuniformities. The model fan is operated, in Freon 12, in a closed loop acoustical facility.
    Keywords: FLUID MECHANICS
    Type: NASA-CR-1831
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Effects of vane/blade ratio and spacing on fan noise (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The effects of vane/blade ratio and spacing on fan noise are investigated to develop a fan noise prediction scheme which is calibrated against experimental data. A 44 blade, 0.504 diameter fan is used to demonstrate the production of fan noise data free from excess noise caused by rotor turbulence interaction. Two stator sets consisting of a cut-off set with 86 vanes, and a cut-on set of 48 vanes are used, with a total range of spacing from 0.5 to 2.3 rotor chords. The model includes viscous wake interaction noise and the potential field interactions of both the rotor and stator. A free-field acoustic environment is achieved by covering the walls, ceiling and floor with 0.7 m polyurethane foam wedges, providing less than + or - 1 dB standing wave ratio at 200 Hz. Only a 3 dB drop in tone level occurs as the spacing is increased from 0.5 to 2.3 rotor chords, and results indicate that the rotor wakes impinging on the stator vanes are the principal noise source for subsonic rotor speeds.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AIAA PAPER 81-2033 , Aeroacoustics Conference; Oct 05, 1981 - Oct 07, 1981; Palo Alto, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Basic research in fan source noise: Inlet distortion and turbulence noise (1978)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A widely recognized problem in jet engine fan noise is the discrepancy between inflight and static tests. This discrepancy consists of blade passing frequency tones, caused by ingested turbulence that appear in the static tests but not in flight. To reduce the ingested distortions and turbulence in an anechoic chamber, a reverse cone inlet is used to guide the air into the fan. This inlet also has provisions for boundary layer suction and is used in conjunction with a turbulence control structure (TCS) to condition the air impinging on the fan. The program was very successful in reducing the ingested turbulence, to the point where reductions in the acoustic power at blade passing frequency are as high as 18 db for subsonic tip speeds. Even with this large subsonic tone suppression, the supersonic tip speed tonal content remains largely unchanged, indicating that the TCS did not appreciably attenuate the noise but effects the generation via turbulence reduction. Turbulence mapping of the inlet confirmed that the tone reductions are due to a reduction in turbulence, as the low frequency power spectra of the streamwise and transverse turbulence were reduced by up to ten times and 100 times, respectively.
    Keywords: ACOUSTICS
    Type: NASA-CR-159451 , SRD-78-186
    Format: application/pdf
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  • 4
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    Effects of vane/blade ratio and spacing on fan noise. Volume 2: Data supplement (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Complete tabulations of 1/3-octave band acoustic measurements are given.
    Keywords: ACOUSTICS
    Type: NASA-CR-174665 , NAS 1.26:174665 , GE-84SRD006-VOL-2 , DS-3-VOL-2
    Format: application/pdf
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  • 5
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    Effects of vane/blade ratio and spacing on fan noise, volume 1 (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The noise characteristics of a high-speed fan were studied. The experimental investigation was carried out on a 50.8 cm (20 in.) diameter scale model fan stage in an anechoic chamber with an inflow turbulence control screen installed. The forty-four blade rotor was tested with forty-eight vane and eighty-six vane stator rows, over a range of aixal rotor-stator spacings from 0.5 to 2.3 rotor tip chords. A two-dimensional strip theory model of rotor-stator interaction noise was employed to predict the measured tone power level trends, and good overall agreement with measured trends was obtained.
    Keywords: ACOUSTICS
    Type: NASA-CR-174664 , NAS 1.26:174664 , GE-84SRD006-VOL-1
    Format: application/pdf
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  • 6
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    The theoretical and experimental investigations on multiple pure tone noise. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An investigation on multiple pure tone (MPT) noise is described. The model fan is operated, in Freon 12, in a closed loop acoustical facility. It has been found experimentally that the rotor relative Mach number and incidence angle are parameters important to the evolution of the MPT sound and the inlet duct length has a significant influence on the MPT sound emission. The experimental results are compared with a previous analysis. From the known blade nonuniformities of the model fan, the MPT distributions are computed. The analysis correctly predicts the frequency of the dominant multiple pure tone and sound pressures of the blade passing frequency noise and the dominant MPT that are in the same range as the experimental values.
    Keywords: PROPULSION SYSTEMS
    Type: AIAA PAPER 72-127 , American Institute of Aeronautics and Astronautics, Aerospace Sciences Meeting; Jan 17, 1972 - Jan 19, 1972; San Diego, CA
    Format: text
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  • 7
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    Reduction of rotor-turbulence interaction noise in static fan noise testing (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Three effective inlet cleanup methods are described. A flared reverse cone inlet is used to eliminate wakes from the fan casings and/or probe supports. Boundary layer suction is employed ahead of the fan rotor and on the outer flare of the cone to reduce the boundary layer turbulence and remove any residual wakes. To reduce the midstream turbulent intensity and length scales, a turbulence control structure is used which is constructed with both a layer of honeycomb and a fine mesh screen. The effects of these cleanup methods are quantified by measuring the far-field noise in an anechoic chamber, using a high-speed 20-in.-diam fan of the current high passband type. The changes in the turbulent field impinging on this rotor are quantified by mapping the streamwise and transverse turbulent properties (spectra, intensity and length scale) with crossed hot film probes. It is convincingly shown that it is possible to clean up the inlet flow of a static fan noise test facility to a point where the static acoustic data simulate flight data.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AIAA PAPER 79-0656 , American Institute of Aeronautics and Astronautics, Aeroacoustics Conference; Mar 12, 1979 - Mar 14, 1979; Seattle, WA
    Format: text
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