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  • 1
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    Application of the Bernoulli enthalpy concept to the study of vortex noise and jet impingement noise (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A complete theory of aeroacoustics of homentropic fluid media is developed and compared with previous theories. The theory is applied to study the interaction of sound with vortex flows, for the DC-9 in a standard take-off configuration. The maximum engine-wake interference noise is estimated to be 3 or 4 db in the ground plane. It is shown that the noise produced by a corotating vortex pair departs significantly from the compact M scaling law for eddy Mach numbers (M) greater than 0.1. An estimate of jet impingement noise is given that is in qualitative agreement with experimental results. The increased noise results primarily from the nonuniform acceleration of turbulent eddies through the stagnation point flow. It is shown that the corotating vortex pair can be excited or de-excited by an externally applied sound field. The model is used to qualitatively explain experimental results on excited jets.
    Keywords: ACOUSTICS
    Type: NASA-CR-2987
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    A study of scattering, production, and stimulated emission of sound by vortex flows (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The basic theory of aeroacoustics of homentropic fluid media is applied to the problems of sound scattering, production, and stimulated emission. A general theory of scattering from low speed three-dimensional vortex flows is presented. Specific results are given for the horseshoe vortex and vortex ring. The noise of an elementary corotating vortex pair in various flows is calculated. It is shown that a potential flow and shear flow can substantially increase the basic pair noise. Small reverse shears can annihilate vortex pairs and eliminate the pair noise mechanism. The pair results are used to explain qualitatively the operation of noise suppression devices. The stimulated emission of a single vortex pair and four and six vortex arrays is demonstrated. The results for six vortices illustrate how external pure tones can amplify the broadband noise of a jet in agreement with recent experimental evidence.
    Keywords: ACOUSTICS
    Type: NASA-CR-3139 , ARAP-363
    Format: application/pdf
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  • 3
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    A study of production and stimulated emission of sound by vortex flows (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The noise radiated by an elementary corotating vortex pair in a shear flow is calculated. It is shown that a small shear can substantially increase the noise while small reverse shears can annihilate vortex pairs and thus reduce the pair noise mechanism. The resonant excitation of an ensonified vortex pair and the broadband noise amplification of a six vortex cluster is calculated. The results are in qualitative agreement with recent experimental findings on jet broadband noise amplification.
    Keywords: ACOUSTICS
    Type: Mechanics of sound generation in flows; Aug 28, 1979 - Aug 31, 1979; Goettingen
    Format: text
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  • 4
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    Interaction with and production of sound by vortex flows (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A description is presented of an improved version of a comprehensive theory of aeroacoustics which, in its original form, had first been reported by Yates and Sandri (1976). The new theory departs in several basic aspects from the concepts provided by Lighthill (1952), Ribner (1964), and Lilley et al. (1974). A detailed derivation of the theory is given for the case of constant entropy flows, taking into account the production of sound by a 'primary' fluid flow, the processing of sound by a flow, and the effects of sound on a primary flow. An investigation is conducted regarding the processing and the production of sound by vortex flow. Questions related to the excitation of a fluid flow by sound are also considered.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 77-1352 , Aeroacoustics Conference; Oct 03, 1977 - Oct 05, 1977; Atlanta, GA
    Format: text
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