Numerical assessment of the scattering of acoustic waves by turbulent structures

Abstract

The scattering of harmonic sound waves by a single vortex is studied to provide some
insight into the more complex problem of sound scattering by a turbulent layer. Two
different methods are used to model the scattering by a steady vortex or by a vortex
convected in a uniform mean flow. The first method is based on the linearized Euler
equations in the frequency domain and is used to study the scattering by a steady vortex.
The speed of this method allows to perform a study of the spatial scattering of a plane
wave over a wide range of frequencies, where analytical models previously developed are
restricted either to low or high frequencies. The second method uses a finite difference
solver, also based on the linearized Euler equations but in the time domain. This method
is used to study the scattering by a vortex convected in a uniform mean fow, where a
spectral scattering occurs in addition to the spatial scattering. A parametric study is
realized, focusing on four parameters including the source frequency and the convection velocity. The spectra deduced from this study show a pattern similar to the haystacking
observed in existing studies of the scattering by a turbulent shear layer. Some of the trends deduced from the parametric study are also in agreement with these previous observations. Thus, the detailled study of the scattering by a single eddy is able to provide further understanding of the turbulence scattering.

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