Abstract
The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent
jet are investigated by direct numerical simulation. Details of the numerical method
are briefly outlined and results are validated against an experiment at the same flow
conditions (Stromberg, McLaughlin & Troutt 1980). Lighthill's theory is used to define
a nominal acoustic source in the jet, and a numerical solution of Lighthill's equation
is compared to the simulation to verify the computational procedures. The acoustic
source is Fourier transformed in the axial coordinate and time and then filtered in
order to identify and separate components capable of radiating to the far field. This
procedure indicates that the peak radiating component of the source is coincident
with neither the peak of the full unfiltered source nor that of the turbulent kinetic
energy. The phase velocities of significant components range from approximately 5%
to 50% of the ambient sound speed which calls into question the commonly made
assumption that the noise sources convect at a single velocity. Space–time correlations
demonstrate that the sources are not acoustically compact in the streamwise direction
and that the portion of the source that radiates at angles greater than 45° is stationary.
Filtering non-radiating wavenumber components of the source at single frequencies
reveals that a simple modulated wave forms for the source, as might be predicted by
linear stability analysis. At small angles from the jet axis the noise from these modes
is highly directional, better described by an exponential than a standard Doppler
factor.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
525 articles.
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