Noise Generation by Cylindrical Spoilers Immersed in an Air Duct.

摘要

The report describes a study concerned with the effect of thin cylindrical flow spoilers upstream of the exit plane of a constant-area duct on the acoustic power output and directivity patterns of the noise field external to the duct. Spoilers of diameter 1/16, 5/32,and 3/16in. were placed at 1/8in. and 11in. from the exit plane of a 1in. diameter duct. Far-field sound pressure levels were measured in an anechoic chamber over a mean velocity range of 250to 900ft/s. The frequency range of the investigation was 200Hz to 50kHz,while the Reynolds number range,based on mean velocity upstream of the spoiler and on spoiler diameter,was 8000to 80,000. (Modified author abstract)