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  • 1
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    Data analysis and noise prediction for the QF-1B experimental fan stage (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The results of a fan noise data analysis and prediction effort using experimental data obtained from tests on the QF-1B research fan are described. Surface pressure measurements were made with flush mounted sensors installed on selected rotor blades and stator vanes and noise measurements were made by microphones located at the far field. Power spectral density analysis, time history studies, and calculation of coherence functions were made. The emphasis of these studies was on the characteristics of tones in the spectra. The amplitude behavior of spectral tones was found to have a large, often predominant, random component, suggesting that turbulent processes play an important role in the generation of tonal as well as broadband noise. Inputs from the data analysis were used in a prediction method which assumes that acoustic dipoles, produced by unsteady blade and van forces, are the important source of fan noise.
    Keywords: ACOUSTICS
    Type: NASA-CR-135066 , BBN-3338
    Format: application/pdf
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  • 2
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    Evaluation of aero Commander propeller acoustic data: Static operations (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Acoustic data are analyzed from a series of ground tests performed on an Aero Commander propeller-driven aircraft with an array of microphones flush-mounted on one side of the fuselage. The analyses were concerned with the propeller blade passage noise during static operation at several different engine speeds and included calculations of the magnitude and phase of the blade passage tones, the amplitude stability of the tones, and the spatial phase and coherence of the tones. The results indicate that the pressure field impinging on the fuselage represents primarily aerodynamic (near field) effects in the plane of the propeller at all frequencies. Forward and aft of the propeller plane aerodynamic effects still dominate the pressure field at frequencies below 200 Hz; but at higher frequencies, the pressure field is due to acoustic propagation from an equivalent center located about 0.15 to 0.30 blade diameters inboard from the propeller hub.
    Keywords: ACOUSTICS
    Type: NASA-CR-158919
    Format: application/pdf
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  • 3
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    Experimental studies of the Space Shuttle payload acoustic environment (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Two series of experiments were conducted to reduce the uncertainties concerning the Space Shuttle payload bay acoustic environment. Tests using a one-fifth scale model showed large changes in level below 125 Hz with the introduction of typical payloads. The changes were associated with particular acoustic modal behavior and were sensitive to the type of acoustic excitation. Another series of experiments evaluated the noise reduction of the first orbiter vehicle (OV-101). The results showed consistently greater noise reduction for grazing excitation than for diffuse excitation. The results were extrapolated to OV-102 using mass law relations and acceleration measurements.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: SAE PAPER 770973 , Aerospace Meeting; Nov 14, 1977 - Nov 17, 1977; Los Angeles, CA
    Format: text
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  • 4
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    Evaluation of aero commander propeller acoustic data: Taxi operations (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The acoustic data from ground tests performed on an Aero Commander propeller driven aircraft are analyzed. An array of microphones flush mounted on the side of the fuselage were used to record data. The propeller blade passage noise during operations at several different taxi speeds is considered and calculations of the magnitude and phase of the blade passage tones, the amplitude stability of the tones, and the spatial phase and coherence of the tones are included. The measured results are compared to theoretical predictions for propeller noise and various evaluations which reveal important details of propeller noise characteristics are presented.
    Keywords: ACOUSTICS
    Type: NASA-CR-159124
    Format: application/pdf
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  • 5
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    Use of coherence and phase data between two receivers in evaluation of noise environments (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: For certain types of noise control problems, where transducers cannot be mounted on suspected sources, valuable information can often be obtained by comparing the coherence and phase data measured between two closely spaced microphones with analytical models deduced from the physics of the problem. However, the application of such analysis techniques must be pursued with care, particularly when the measurements are made in a reverberant area. A simple illustration is presented where the acoustic field in the test section of a wind tunnel is evaluated by modelling the field as a combination of diffuse noise due to the boundary layer turbulence in the test section and propagating noise generated by the tunnel fan and possible flow disturbances outside the test section. The coherence and phase between two closely spaced microphones in the tunnel test section are predicted for various ratios of diffuse to propagating noise contributions and compared to actual measurements under several different tunnel operating conditions.
    Keywords: ACOUSTICS
    Type: Journal of Sound and Vibration; 56; Jan. 22
    Format: text
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  • 6
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    Coherence and phase techniques applied to noise diagnosis in the NASA Ames 7 times 10-foot wind tunnel no. 1 (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Measurements have been made of coherence and phase spectra for the acoustic field in a subsonic wind tunnel. The data are interpreted in terms of simple analytical models for propagating and diffuse noise fields, including the presence of uncorrelated noise signals. It is found that low frequency noise propagates upstream and downstream from the fan, with the noise in the test section arriving in the upstream direction. High frequency sound is generated in the test section and propagates upstream and downstream. In the low frequency range, the ratio of diffuse to propagating energy is about eight for all locations in the test section, diffuser, and settling chamber; the value of the ratio increases with frequency.
    Keywords: ACOUSTICS
    Type: NASA-CR-152039 , BBN-3559
    Format: application/pdf
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  • 7
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    Shuttle bay acoustics (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Acoustic energy generated during Shuttle liftoff will propagate up the orbiter vehicle, transmit through the payload bay structure, and produce an intense acoustic field inside the bay with the potential for damaging relatively fragile payload components. This paper describes three experimental programs aimed at investigating Shuttle bay acoustics. The first two experiments, conducted in July 1976 and January 1977 respectively, were concerned primarily with establishing the noise reduction of the OV101 payload bay structure; the third set of experiments, carried out during April and May 1978, was concerned with the influence of payloads on the bay acoustic levels. Test results are summarized, and comparisons with analytical model predictions are presented.
    Keywords: SPACE TRANSPORTATION
    Type: Aerospace Testing Seminar; Sep 19, 1979 - Sep 21, 1979; Los Angeles, CA
    Format: text
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  • 8
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    Coherence and phase techniques applied to wind tunnel acoustics (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Measurements have been made of coherence and phase spectra for the acoustic field in a subsonic wind tunnel. The data are interpreted in terms of simple analytical models for propagating and diffuse noise fields, including the presence of uncorrelated noise signals. It is found that low frequency noise propagates upstream and downstream from the fan, with the noise in the test section arriving in the upstream direction. High frequency sound appears to be generated in the test section and propagates upstream and downstream. In the low frequency range, the ratio of diffuse to propagating energy is about 8 for all locations in the test section, diffuser, and settling chamber; the value of the ratio increases with frequency. Further analysis is required to describe in better detail the effects of reverberation and incoherent sources in a duct-like environment.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 77-1306 , Aeroacoustics Conference; Oct 03, 1977 - Oct 05, 1977; Atlanta, GA
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Characteristics of propeller noise on an aircraft fuselage related to interior noise transmission (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Exterior noise was measured on the fuselage of a twin-engine, light aircraft at four values of engine rpm in ground static tests and at forward speeds up to 36 m/s in taxi tests. Propeller noise levels, spectra, and correlations were determined using a horizontal array of seven flush-mounted microphones and a vertical array of four flush-mounted microphones in the propeller plane. The measured levels and spectra are compared with predictions based on empirical and analytical methods for static and taxi conditions. Trace wavelengths of the propeller noise field, obtained from point-to-point correlations, are compared with the aircraft sidewall structural dimensions, and some analytical results are presented that suggest the sensitivity of interior noise transmission to variations of the propeller noise characteristics.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 79-0646 , American Institute of Aeronautics and Astronautics, Aeroacoustics Conference; Mar 12, 1979 - Mar 14, 1979; Seattle, WA
    Format: text
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