REFRACTION OF SOUND BY JET FLOW AND JET TEMPERATURE II.
TORONTO UNIV (ONTARIO) INST FOR AEROSPACE STUDIES
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The refraction of the sound field of an omnidirectional pure tone point source of sound by the temperature and velocity fields of a 34 inch air or nitrogen jet was measured. Several source positions were employed one within the potential core, others entirely outside the jet. For the source in the on-axis position, the air jet velocity was varied between M 0.5 and 0.95 at fixed source frequency and ambient jet temperature, yielding a characteristic axial refraction valley, e.g., -35dB at M 0.95 and 3000 c.p.s. Similar, but asymmetric patterns were obtained with the source outside the jet. Using a very cold nitrogen jet T -180C, the sound was found to be refracted inward - a focusing effect - to yield an intensity lobe along the jet axis e.g. 26dB at M 0.11 and 7000 c.p.s. For both the cold jet and the ambient jet the ordinary jet noise was measured in narrow filter bands the respective polar plots exhibited the same general shape near the axis as those for the injected pure tones. The filtered jet noise polar plots were also corrected for refraction using the pure-tone patterns and for convection via theory to yield the approximate basic directivity of the eddy sources the polar patterns resemble ellipses of low eccentricity, rather unlike Lighthills four-leaf-clover. Author
- Fluid Mechanics