The Use of Co-Flowing Airstreams for the Simulation of Flight Effects on Jet Noise,
Abstract
The simulation of in-flight effects on aircraft noise continues to be the subject of much debate. One possible simulation consists of surrounding the air jet emitted from a stationary nozzle with a concentric secondary jet blowing at an appreciably lower velocity representing that of flight. This report describes an investigation of the influence of such a co-flowing airstream on the noise of subsonic air jets over a range of secondary-to-primary area ratios from 1.8 to 1800. Correlations of these data have confirmed that the effects of flight on jet mixing noise may be investigated using a comparatively small secondary stream and with the microphone positioned outside the flow. The results show that a minimum area ratio of about 50 is necessary to model adequately the effects of flight for the main noise-producing regions of the jet. As the size of the secondary stream is reduced, information for the lower frequencies is progressively lost. It is necessary to correct the flight data for the propagation of the sound through the shear layer surrounding the secondary flow. It has been shown that an existing theory is adequate for these corrections; this theory models the shear layer as a cylindrical velocity discontinuity and considers refraction of the sound as the dominant propagation mechanism.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1977
- Accession Number
- ADA044657
Entities
People
- B. J. Cocking
- D. J. Way