Title page for ETD etd-07192007-123339


Type of Document Dissertation
Author Grissom, Dustin Leonard
URN etd-07192007-123339
Title A Study of Sound Generated by a Turbulent Wall Jet Flow Over Rough Surfaces
Degree PhD
Department Aerospace and Ocean Engineering
Advisory Committee
Advisor Name Title
Devenport, William J. Committee Chair
Burdisso, Ricardo A. Committee Member
Glegg, Stewart A. L. Committee Member
Johnson, Martin E. Committee Member
Simpson, Roger L. Committee Member
Keywords
  • turbulent flow noise
  • wall jet
  • rough wall boundary layer noise
  • acoustic scattering
Date of Defense 2007-07-10
Availability unrestricted
Abstract
The far field acoustics generated by turbulent flow over rough surfaces has been experimentally investigated in an acoustically treated wall jet facility. The facility allows direct measurement of the far field sound from small patches of surface roughness, without contamination from edge or other aerodynamic noise sources. The facility is capable of generating turbulent boundary layer flows with momentum thickness Reynolds numbers between 450 and 1160. The variation of surface conditions tested cover the range from hydrodynamically smooth surfaces through most of the transitional range, with h+ variations from 3 to 85. Single microphone narrow band acoustic spectra, measured in the far field, show sound levels as much as 15 dB above the background from 0.186 m2 roughness patches. The measurements revealed the spectral shape and level variations with flow velocity, boundary layer thickness, and roughness size; providing the first data set large enough to assess the affects of many aerodynamic properties on the acoustic spectra. Increases in the size of grit type roughness produced significant increases in acoustic levels. Patches of hydrodynamically smooth roughness generated measurable acoustic levels, confirming that acoustic scattering is at least one of the physical mechanisms responsible for roughness noise. The shapes of the measured spectra show a strong dependence on the form of the surface roughness. The acoustic spectra generated by periodic two-dimensional surfaces have a much narrower louder peak than that generated by three-dimensional grit type roughness. Measurements also show the orientation of the two-dimensional surface significantly affects the acoustic levels and directivity.

The variation of sound levels with flow velocity and roughness size suggests the acoustic field is significantly affected by changes in the near wall flow due to the presence of the roughness. Current models of noise generated by rough surfaces predict the general trends seen in measurements for flows over grit and two-dimensional roughness in the range of 20

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