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  • Other Sources  (14)
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  • 1
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    New broadband shock noise model and computer code for ANOPP (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The basic mechanism for broadband shock noise in supersonic jets is the interaction between the shock waves and the turbulence in the jet exhaust. This source is in addition to jet mixing noise.
    Keywords: ACOUSTICS
    Type: NASA. Langley Research Center, First Annual High-Speed Research Workshop, Part 3; p 1075-1101
    Format: application/pdf
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  • 2
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    Acoustic loads prediction on jet aircraft (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: A nearfield aircraft noise prediction computer program is presented for the F-22 aircraft. The dominant sources of noise are jet turbulent mixing noise, jet broadband shock noise, and fluctuating pressure under the turbulent boundary layer. All results from this investigation are presented in viewgraph format.
    Keywords: ACOUSTICS
    Type: NASA. Langley Research Center, Fourth Aircraft Interior Noise Workshop; p 1-12
    Format: text
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  • 3
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    USB flow characteristics related to noise generation (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The effects of nozzle and flap geometry on upper surface blown flow field characteristics related to noise generation were examined experimentally using static models. Flow attachment and spreading characteristics were observed using flow visualization techniques. Velocity and turbulence profiles in the trailing edge wake were measured using hot-wire anemometry, and the effects of the geometric variables on peak velocity and turbulence intensity were determined. It is shown that peak trailing edge velocity is a function of the ratio of flow length to modified hydraulic diameter.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Res. Center Powered-Lift Aerodyn. and Acoustics; p 213-226
    Format: application/pdf
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  • 4
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    A prediction method for broadband shock associated noise from supersonic rectangualr jets (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Braodband shock associated noise is an important aircraft noise component of the proposed high-speed civil transport (HSCT) at take-offs and landings. For noise certification purpose one would, therefore, like to be able to predict as accurately as possible the intensity, directivity and spectral content of this noise component. The purpose of this work is to develop a semi-empirical prediction method for the broadband shock associated noise from supersonic rectangular jets. The complexity and quality of the noise prediction method are to be similar to those for circular jets. In this paper only the broadband shock associated noise of jets issued from rectangular nozzles with straight side walls is considered. Since many current aircraft propulsion systems have nozzle aspect ratios (at nozzle exit) in the range of 1 to 4, the present study has been confined to nozzles with aspect ratio less than 6. In developing the prediction method the essential physics of the problem are taken into consideration. Since the braodband shock associated noise generation mechanism is the same whether the jet is circular or round the present prediction method in a number of ways is quite similar to that for axisymmetric jets. Comparisons between predictions and measurements for jets with aspect ratio up to 6 will be reported. Efforts will be concentrated on the fly-over plane. However, side line angles and other directions will also be included.
    Keywords: ACOUSTICS
    Type: (ISSN 0736-2935); : The use of EOS for
    Format: text
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  • 5
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    Lateral noise attenuation of the advanced propeller of the propfan test assessment aircraft (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Lateral noise attenuation characteristics of the advanced propeller are determined using the flight test results of the testbed aircraft, Propfan Test Assessment (PTA), with a single, large-scale propfan. The acoustic data were obtained with an array of ground-mounted microphones positioned at distances up to 2.47 km (8100 feet) to the side of the flight path. The aircraft was flown at a Mach number of 0.31 for a variety of operating conditions. The lateral noise attenuation in a frequency range containing the blade passage frequency of the propeller was found to have positive magnitudes on the propfan side and negative magnitudes on the opposite side. The measured attenuation exhibits a strong dependence upon the elevation angle. The results also display a clear dependence upon the angle at which the propeller and nacelle are mounted on the wing (inflow angle).
    Keywords: ACOUSTICS
    Type: AIAA PAPER 89-1057
    Format: text
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  • 6
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    Installed propfan (SR-7L) far-field noise characteristics (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Far-field noise characteristics of the SR-7L single-rotor propfan were obtained from the Propfan Test Assessment (PTA) aircraft flight tests. The aircraft was flown at low altitudes (about 310m) above the ground at a constant speed of about 92 m/sec. The acoustic data were acquired with an array of ground-flush microphones positioned on both sides of the flight path. Propfan-generated noise levels were extracted from the total aircraft noise, and these data were then used to study the far-field noise characteristics. The directivities at the polar and azimuthal planes, and the variations of the blade-order tone levels with propfan power and blade tip Mach number were derived. The effect of inflow angle was studied by changing the nacelle tilt angle. The levels and the directivity were very sensitive to the nacelle tilt angle (i.e., inflow angle). The noise levels in the aft quadrant were found to be higher than in the forward quadrant. Also, the noise levels on the starboard side of the aircraft were found to be higher than on the port side. The noise levels increase with propfan power and rotational speed.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 89-1056
    Format: text
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  • 7
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    Radiated noise from an externally blown flap (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The far field noise from subsonic jet impingement on a wing-flap with a 45 deg bend was experimentally investigated. The test parameters are jet Mach number and flap length. For long flaps, the primary source mechanisms are found to be turbulent mixing and flow impingement. For short flaps, the interaction of turbulent flow with the flap trailing edge appears to strongly influence the radiated noise.
    Keywords: ACOUSTICS
    Type: NASA-TN-D-7908 , L-9895
    Format: application/pdf
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  • 8
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    Analytical developments for definition and prediction of USB noise (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A systematic acoustic data base and associated flow data are used in identifying the noise generating mechanisms of upper surface blown flap configurations of short takeoff and landing aircraft. Theory is developed for the radiated sound field of the highly sheared flow of the trailing edge wake. An empirical method is also developed using extensive experimental data and physical reasonings to predict the noise levels.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Res. Center Powered-Lift Aerodyn. and Acoustics; p 241-262
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  • 9
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    Propfan Test Assessment (PTA): Flight test report (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Propfan Test Assessment (PTA) aircraft was flown to obtain glade stress and noise data for a 2.74m (9 ft.) diameter single rotation propfan. Tests were performed at Mach numbers to 0.85 and altitudes to 12,192m (40,000 ft.). The propfan was well-behaved structurally over the entire flight envelope, demonstrating that the blade design technology was completely adequate. Noise data were characterized by strong signals at blade passage frequency and up to 10 harmonics. Cabin noise was not so high as to preclude attainment of comfortable levels with suitable wall treatment. Community noise was not excessive.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-182278 , NAS 1.26:182278 , LG89ER0026
    Format: application/pdf
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  • 10
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    Trailing edge wake flow characteristics of upper surface blown configurations (1978)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Mean and fluctuating flow characteristics in the wake of upper surface blown flap configurations are presented. Relative importance of the longitudinal and the transverse components of the wake flow turbulence for noise generation are evaluated using correlation between the near-field noise and the wake turbulence. Effects of the jet velocity, the initial turbulence in the jet, and the flap deflection angle on noise and wake flow characteristics are studied. The far-field noise data is compared with the existing empirical prediction method. The measured wake flow properties are compared with an analytical model used in the existing USB wake flow noise theory. The detailed wake flow profiles, wake flow turbulence space-time correlations, wake flow turbulence cross-power spectra, and near-field noise third octave band spectra are presented in the appendices.
    Keywords: AERODYNAMICS
    Type: NASA-CR-152224 , LG78ER0252
    Format: application/pdf
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