A computational approach to the prediction of jet mixing noise
is
described. It is based
on Lighthill's analogy, used together with a semi-deterministic modelling
of turbulence
(SDM), where only the large-scale coherent motion is evaluated. The features
of SDM
are briefly illustrated in the case of shear layers, showing that suitable
descriptions
of the mean flow and of the large-scale fluctuations are obtained. Aerodynamic
calculations of two cold fully expanded plane jets at Mach numbers 0.50
and 1.33 are
then carried out. The numerical implementation of Lighthill's analogy
is
described and
different integral formulations are compared for the two jets. It is shown
that
the one
expressed in a space–time conjugate (κ, ω)-plane is particularly
convenient and allows
a simple geometrical interpretation of the computations. Acoustic results
obtained
with this formulation are compared to relevant experimental data. It is
concluded
that the radiation of subsonic jets cannot be explained only by the contribution
of the turbulent coherent motion. In this case, directivity effects are
well
recovered but the
acoustic spectra are too narrow and limited to the low-frequency range.
In contrast
at Mach number 1.33, especially in the forward quadrant, results are satisfactory,
showing that coherent structures indeed provide the main source of supersonic
jet
mixing noise.
Wavepacket models for supersonic jet noise
