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  • ACOUSTICS  (2)
  • AERODYNAMICS  (1)
  • GEOPHYSICS
  • Polymer and Materials Science
  • 1985-1989  (4)
  • 1989  (4)
  • 1
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    Time dependent inflow-outflow boundary conditions for 2D acoustic systems (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An analysis of the number and form of the required inflow-outflow boundary conditions for the full two-dimensional time-dependent nonlinear acoustic system in subsonic mean flow is performed. The explicit predictor-corrector method of MacCormack (1969) is used. The methodology is tested on both uniform and sheared mean flows with plane and nonplanar sources. Results show that the acoustic system requires three physical boundary conditions on the inflow and one on the outflow boundary. The most natural choice for the inflow boundary conditions is judged to be a specification of the vorticity, the normal acoustic impedance, and a pressure gradient-density gradient relationship normal to the boundary. Specification of the acoustic pressure at the outflow boundary along with these inflow boundary conditions is found to give consistent reliable results. A set of boundary conditions developed earlier, which were intended to be nonreflecting is tested using the current method and is shown to yield unstable results for nonplanar acoustic waves.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 89-1041
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Flow measurement on the fuselage of a Boeing 737 airplane (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Results are presented on flow measurements on the fuselage of a Boeing 737 aircraft, carried out during flight tests. The instruments used to measure static pressure, local skin friction, boundary layer characteristics, turbulence properties, and pressure fluctuations are described together with the computational methods used. Boundary layer thicknesses were found to be typically 6-8 inches at Reynolds numbers based on the momentum thickness of 60-180,000, depending on flight conditions and location along the fuselage.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-0209
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Design curves for circular and annular duct silencers (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Conventional models of sound propagation between porous walls (Scott, 1946) are adapted in order to calculate design curves for the lined circular and annular-duct silencers used in HVAC systems. The derivation of the governing equations is outlined, and results for two typical cases are presented graphically. Good agreement with published experimental data is demonstrated.
    Keywords: ACOUSTICS
    Type: International Conference on Noise Control Engineering; Dec 04, 1989 - Dec 06, 1989; Newport Beach, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    The planning and execution of ER-2 and DC-8 aircraft flights over Antarctica, August and September 1987 (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The significant ozone loss in the lower stratosphere over Antarctica during recent austral springs was studied by instrumented ER-2 and DC-8 aircraft. Data on the homogeneous gas composition, polar stratospheric clouds, and on tracers for dynamic motion are provided. The mission design is described, the aircraft and their payloads are documented, and the flight tracks are specified.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 11181-11
    Format: text
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    NASA TECHNICAL REPORTS
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