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  • 1
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    Acoustic propagation in ducts with varying cross sections and sheared mean flow. (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An analysis is presented of the wave propagation and attenuation in two-dimensional ducts with slowly varying cross sections which carry sheared mean flow. A uniformly valid asymptotic expansion of the acoustic waves is obtained in terms of the maximum slope of the wall by using the method of multiple scales. The result is a first-order differential equation describing the amplitude variation with the axial distance. This equation is used to evaluate the effects of variations of the duct cross section and growing boundary layers on the different acoustic modes.
    Keywords: FLUID MECHANICS
    Type: AIAA PAPER 73-1008 , Aero-Acoustics Conference; Oct 15, 1973 - Oct 17, 1973; Seattle, WA
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Effect of the acoustic boundary layer on the wave propagation in ducts (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An analysis is presented for the wave propagation in two-dimensional and circular lined ducts taking into account the effects of viscosity in both the mean and the acoustic problems. The method of composite expansions is used to express each acoustic flow quantity as the sum of an inviscid part and a boundary layer part insignificant outside a thin layer next to the wall. The problem is reduced to solving a second-order ordinary differential equation for the pressure perturbation as in the inviscid acoustic case but with a modified specific wall admittance. An analytic expression is presented for the variation of the modified admittance with the wall and flow parameters, such as the acoustic boundary layer thickness, the mean velocity and temperature gradients at the wall, the frequency of oscillation, and the wavelength.
    Keywords: FLUID MECHANICS
    Type: Acoustical Society of America; vol. 54
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Effect of bulk-reacting liners on wave propagation in ducts. (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Keywords: FLUID MECHANICS
    Type: AIAA PAPER 73-227 , Aerospace Sciences Meeting; Jan 10, 1973 - Jan 12, 1973; Washington, DC
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Transmission of sound through annular ducts of varying cross sections and sheared mean flow (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An asymptotic solution is presented for the transmission and attenuation of acoustic waves in an annular duct of slowly varying cross section which carries a sheared mean flow. The analysis also takes into account the growth of the boundary layer as well as any slow variations in the acoustic liner properties. The problem is reduced to the solution of a first-order ordinary differential equation for the amplitude. The analysis is used to estimate the effects of the variations of the duct cross section and boundary layer growth on the different acoustic modes.
    Keywords: FLUID MECHANICS
    Type: AIAA PAPER 74-58 , Aerospace Sciences Meeting; Jan 30, 1974 - Feb 01, 1974; Washington, DC
    Format: text
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
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