Accession Number : ADA618611


Title :   Jet Crackle


Descriptive Note : Final rept. 15 Aug 2010-14 Feb 2015


Corporate Author : ILLINOIS UNIV AT URBANA-CHAMPAIGN DEPT OF MECHANICAL SCIENCE AND ENGINEERING


Personal Author(s) : Freund, Jonathan B ; Buchta, David A


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a618611.pdf


Report Date : 23 Jun 2015


Pagination or Media Count : 49


Abstract : Fighter jets and other aircraft with high specific thrust engines can make a particularly intense type of noise that has come to be called crackle. It is unmistakably different than lower speed jet noise. Its frequency content, extreme intensity, and sporadic character make it particularly annoying and potentially injurious to insufficiently protected hearing. We have complete a set of detailed direct numerical simulations of free shear flows to investigate turbulence as a source of jet crackle. This report includes (1) detailed documentation of these simulations, (2) their verification and validation, (3) and several post-processing investigation the underlying mechanics of jet crackle, including detailed quantification of the near acoustic field, analysis of statistical metrics of jet crackle, analysis of sound-field nonlinear effects, and the relation of crackle to the linear instability modes supported by free shear flows. This is the first-ever such detailed investigation of these mechanisms.


Descriptors :   *ACOUSTIC FIELDS , *JET AIRCRAFT NOISE , *SHEAR FLOW , *STATISTICS , *TURBULENCE , DISCRETE FOURIER TRANSFORMS , EQUATIONS , FINITE DIFFERENCE THEORY , HIGH VELOCITY , INSTABILITY , LAYERS , MACH NUMBER , METRICS , NEAR FIELD , NUMERICAL METHODS AND PROCEDURES , PRESSURE , REYNOLDS NUMBER , SIMULATION , SKEWNESS


Subject Categories : Numerical Mathematics
      Statistics and Probability
      Acoustics
      Fluid Mechanics


Distribution Statement : APPROVED FOR PUBLIC RELEASE