Acoustical Diffraction Radiation.
STANFORD UNIV CALIF DEPT OF MATHEMATICS
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A finite region of turbulent flow is represented by a volume distribution of quadrupolar sources, according to the Lighthill model, for the purpose of estimating the sound level generated in the surrounding region. By way of incorporating environmental features into such a model of free turbulence it becomes appropriate to examine quadrupolar source interaction with material surfaces this poses a formidable diffraction or scattering problem unless the surface is compact on the acoustic wave length scale or of simple geometrical shape. The calculations by Ffowcs Williams and Hall 1970, Crighton and Leppington 1971 relative to an immobile point quadrupole near the straight edge of a thin semi-infinite plane screen, which bring out the possibility of a substantial amplification in the far field as the result of scattering by the screen, suggest a related rise for the output level of an actual flow in a comparable setting and they prompt the consideration of acoustical effects attributable to the motion of sources past the edge. Author
- Fluid Mechanics