QUADRUPOLE CORRELATIONS GOVERNING THE PATTERN OF JET NOISE.
TORONTO UNIV (ONTARIO) INST FOR AEROSPACE STUDIES
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The effects of convection and refraction dominate the heart-shaped pattern of jet noise. These can be corrected out to yield the basic directivity of the eddy noise generators. The observed quasi-ellipsoidal pattern was predicted by Ribner 1963, 1964 in a variant of the Lighthill theory, postulating isotropic turbulence superposed on a mean shear flow. This had the feature of dealing with the joint effects of the quadrupoles without displaying them individually. The paper reformulates the theory so as to calculate the relative contributions of the different quadrupole self- and cross-correlations to the sound emitted in a given direction. Spectra are also discussed, following the earlier work. Finally, the predictions are shown to be compatible with recent experimental results. Of the 36 possible quadrupole correlations only 9 yield distinct nonzero contributions to the axisymmetric noise pattern of a round jet. The individual directional patterns have either 2 or 4 lobes, but they combine to yield a quasi-ellipsoidal overall pattern basic directivity before convection or refraction are allowed for. This is compounded of partial patterns called self-noise and shear-noise. Author
- Fluid Mechanics