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  • 1
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    A parametric study of the effect of inlet lip shape upon the radiated sound field (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Far field sound radiation predictions for four different axisymmetric inlet lips excited by different tangential acoustic modes at several cut-off ratios are presented. These results were obtained by numerical integration of a special cylindrically symmetric integral representation of the external solutions of the Helmholtz equation which yields unique solutions at all wave numbers. The paper presents plots which detail the dependence of the relative SPL (dB) in the field upon the engine inlet lip shape, the modal input, and the cut-off ratio. Examination of these data indicate that: (1) as the inlet lip becomes larger the predominant acoustic radiation peak in the field becomes narrower and moves towards the centerline of the inlet; (2) as the order of the tangential acoustic mode of the driver increases the radiated sound peak again becomes narrower but moves away from the inlet centerline; and (3) as the cut-off ratio is increased for a specific tangential acoustic mode the predominant radiation peak becomes narrower and moves towards the centerline of the inlet.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 84-0498
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    A theoretical investigation of the sound radiation fields associated with a Bellmouth inlet (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Analytical results are obtained by numerical integration of a cylindrically symmetric integral representation of the external solutions of the Helmholtz equation. The accuracy of this method is checked by comparisons of computed results with 'exact' solutions generated by the point source method. In all cases, the average error for the amplitude and phase of the points calculated in the field is found to be less than ten percent. Theoretical studies which model experiments run for the NASA Langely Bellmouth inlet configuration are presented and comparisons are made with the experimental results. In all cases very good agreement is obtained between the experimental and theoretically calculated values.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 83-0710 , American Institute of Aeronautics and Astronautics, Aeroacoustics Conference; Apr 11, 1983 - Apr 13, 1983; Atlanta, GA
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Prediction of sound radiation from different practical jet engine inlets (1982)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Computer codes which were based upon a special integral representation of the external solutions of the Helmholtz equation were upgraded so that they would yield accurate results for the acoustic radiation patterns in the field surrounding an axisymmetric body for nondimensional wave numbers, based on duct radius, of up to twenty. The accuracy of these computer programs was checked by the use of the point source method for the generation of exact solutions and then by comparison with the results of other experimental and theoretical studies. These computer codes were used in a parametric study of the dependence of the radiated sound field on input modal distribution, wave number, and inlet lip shape. The results of this study show that: (1) as the wave number (i.e., cut off ratio) is increased for a given input modal distribution that the acoustic radiation peak moves towards the inlet centerline and becomes more compact (i.e., narrows); (2) as the input mode number is increased for a given cut off ratio the acoustic radiation peak moves away from the inlet centerline and becomes more compact.
    Keywords: ACOUSTICS
    Type: NASA-CR-169533 , NAS 1.26:169533
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Prediction of sound radiation from different practical jet engine inlets (1982)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The computer codes necessary for this study were developed and checked against exact solutions generated by the point source method using the NASA Lewis QCSEE inlet geometry. These computer codes were used to predict the acoustic properties of the following five inlet configurations: the NASA Langley Bellmouth, the NASA Lewis JT15D-1 Ground Test Nacelle, and three finite hyperbolic inlets of 50, 70 and 90 degrees. Thirty-five computer runs were done for the NASA Langley Bellmouth. For each of these computer runs, the reflection coefficient at the duct exit plane was calculated as was the far field radiation pattern. These results are presented in both graphical and tabular form with many of the results cross plotted so that trends in the results verses cut-off ratio (wave number) and tangential mode number may be easily identified.
    Keywords: ACOUSTICS
    Type: NASA-CR-165120
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Prediction of sound radiation from different practical jet engine inlets (1981)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Computer codes, capable of producing accurate results for nondimensional wave numbers (based on duct radius) of up to 20, were developed and used to generate results for various other inlet configurations. Both reflection coefficients and radiation patterns were calculated by the integral solution procedure for the following five inlet configurations: the NASA Langley Bellmouth, the NASA Lewis JT-15D-1 ground test nacelle, and three hyperbolic inlets of 50, 70, and 90 degrees. Results obtained are compared with results from other experimental and theoretical studies.
    Keywords: ACOUSTICS
    Type: NASA-CR-164620
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Prediction of sound radiated from different practical jet engine inlets (1980)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Existing computer codes for calculating the far field radiation patterns surrounding various practical jet engine inlet configurations under different excitation conditions were upgraded. The computer codes were refined and expanded so that they are now more efficient computationally by a factor of about three and they are now capable of producing accurate results up to nondimensional wave numbers of twenty. Computer programs were also developed to help generate accurate geometrical representations of the inlets to be investigated. This data is required as input for the computer programs which calculate the sound fields. This new geometry generating computer program considerably reduces the time required to generate the input data which was one of the most time consuming steps in the process. The results of sample runs using the NASA-Lewis QCSEE inlet are presented and comparison of run times and accuracy are made between the old and upgraded computer codes. The overall accuracy of the computations is determined by comparison of the results of the computations with simple source solutions.
    Keywords: ACOUSTICS
    Type: NASA-CR-163824
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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