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  • 1
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    Computing aerodynamic sound using advanced statistical turbulence theories (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: It is noted that the calculation of turbulence-generated aerodynamic sound requires knowledge of the spatial and temporal variation of Q sub ij (xi sub k, tau), the two-point, two-time turbulent velocity correlations. A technique is presented to obtain an approximate form of these correlations based on closure of the Reynolds stress equations by modeling of higher order terms. The governing equations for Q sub ij are first developed for a general flow. The case of homogeneous, stationary turbulence in a unidirectional constant shear mean flow is then assumed. The required closure form for Q sub ij is selected which is capable of qualitatively reproducing experimentally observed behavior. This form contains separation time dependent scale factors as parameters and depends explicitly on spatial separation. The approximate forms of Q sub ij are used in the differential equations and integral moments are taken over the spatial domain. The velocity correlations are used in the Lighthill theory of aerodynamic sound by assuming normal joint probability.
    Keywords: ACOUSTICS
    Type: NASA-CR-165697
    Format: application/pdf
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  • 2
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    Predicting aerodynamic sound utilizing a two-point, two-time turbulence theory (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The feasibility of determining two-point, two-time turbulent velocity correlations based on extending closure models for one-point, one-time turbulence correlations is demonstrated. The procedure used is based on a spatial moment integral formulation of the governing equations using approximate, parameterized trial functions for the two-point, two-time velocity correlations. Solution of the equations is shown to give a set of anisotropic length scales and the separation-time-dependent decorrelation of the ensemble averaged turbulent velocities. The analysis is simplified using the assumption of homogeneous stationary turbulence and a constant shear, unidirectional mean flow. It is shown that the anisotropic behavior of measured turbulence correlations can be characterized through this technique.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 81-2023 , Aeroacoustics Conference; Oct 05, 1981 - Oct 07, 1981; Palo Alto, CA
    Format: text
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