Accession Number : AD0431323


Title :   JET NOISE,


Corporate Author : ADVISORY GROUP FOR AERONAUTICAL RESEARCH AND DEVELOPMENT PARIS (FRANCE)


Personal Author(s) : Lighthill, M J


Report Date : Apr 1963


Pagination or Media Count : 33


Abstract : The acoustic efficiency of undisintegrated jets (including those associated with aircraft and rockets) depends principally on the ratio M of the jet speed to the atmospheric speed of sound, varying approximately as ten to the minus four power by M to the fifth power for low M but being constant (about 0.006) for high M, and changing from one form to the other rather abruptly around M=2. Improved measurements of jet turbulence and an improved theory of the acoustic radiation from eddies convected at speeds exceeding the atmospheric sound speed are used to show how this form of acoustic efficiency variation, and the associated changes in directional distribution and frequency spectrum, can be explained in terms of a comprehensive theory, which represents a jet as a distribution of acoustic quadrupoles in an otherwise undisturbed atmosphere, the quadrupole strengths being well correlated only within convected eddies of limited extent and limited lifetime. (Author)


Descriptors :   *JET AIRCRAFT NOISE , TURBULENCE , SUBSONIC CHARACTERISTICS , SUBSONIC FLOW , SUPERSONIC CHARACTERISTICS , SUPERSONIC FLOW , ACOUSTICS , JET PROPULSION , ACOUSTIC PROPERTIES


Distribution Statement : APPROVED FOR PUBLIC RELEASE