Accession Number : ADA267027


Title :   Some Aspects of the Aeroacoustics of High-Speed Jets


Descriptive Note : Contractor rept.,


Corporate Author : INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA


Personal Author(s) : Lighthill, James


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a267027.pdf


Report Date : May 1993


Pagination or Media Count : 47


Abstract : The lecture begins by sketching some of the background to contemporary jet aeroacoustics. Then it reviews scaling laws for noise generation by low-Mach-number airflows and by turbulence convected at 'not so low' Mach number. These laws take into account the influence of Doppler effects associated with the convection of aeroacoustic sources. Next, a uniformly valid Doppler-effect approximation exhibits the transition, with increasing Mach number of convection, from compact-source radiation at low Mach numbers to a statistical assemblage of conical shock waves radiated by eddies convected at supersonic speed. In jets, for example, supersonic eddy convection is typically found for jet exit speeds exceeding twice the atmospheric speed of sound. The Lecture continues by describing a new dynamical theory of the nonlinear propagation of such statistically random assemblages of conical shock waves. It is shown, both by a general theoretical analysis and by an illustrative computational study, how their propagation is dominated by a characteristic 'bunching' process. That process-associated with a tendency for shock waves that have already formed unions with other shock waves to acquire an increased proneness to form further unions - acts so as to enhance the high-frequency part of the spectrum of noise emission from jets at these high exit speeds.... Jet acoustics, Nonlinear propagation, Conical shocks, Numerical experiments


Descriptors :   *AERODYNAMICS , *JET AIRCRAFT NOISE , VELOCITY , FREQUENCY , EMISSION , HIGH FREQUENCY , ACOUSTIC WAVES , SHOCK WAVES , AIR FLOW , CONVECTION , TURBULENCE , EDDIES(FLUID MECHANICS) , WAVE PROPAGATION , SOUND , BACKGROUND , ACOUSTICS , TRANSITIONS , NOISE , MACH NUMBER , DOPPLER EFFECT


Subject Categories : Aerodynamics
      Acoustics


Distribution Statement : APPROVED FOR PUBLIC RELEASE