### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 3aPAb7. On the influence of turbulence modeling for atmospheric sound
propagation.

**Ph. Blanc-Benon
**

**
D. Juve
**

**
P. Chevret
**

**
**
*Lab. de Mecanique des Fluides et d'Acoustique, URA CNRS 263, Ecole Centrale
de Lyon, BP 163, 69131 Ecully Cedex, France
*

*
*
Incorporating random aspects in the numerical simulation of atmospheric
sound propagation has led to a much better agreement between experiments and
predictions. In particular, the turbulent scattering of sound into acoustic
shadows had been demonstrated but some discrepancies still exist. In most of the
numerical studies the fluctuations of the refractive index have been considered
as scalar and characterized by a single length scale (Gaussian spectrum).
However, sound propagation in the turbulent atmosphere is affected by quantities
with different tensorial character and different scales. In this paper two
possible ways of improving the simulations are investigated: by choosing a
better spectral representation of the turbulence (von Karman instead of Gaussian
form); by correctly taking into account the vectorial character of wind
fluctuations. The turbulence is represented as a set of realizations of a random
field generated by a limited number of scalar or vectorial random Fourier modes.
Through each individual realization, the acoustic pressure field is computed
with a wide-angle parabolic approximation. Ensemble averaging is then performed
to obtain the statistical properties of the acoustic field: mean level, standard
deviation of the fluctuations. Illustrations will be given for an upward
refracting atmosphere, when a deep deterministic shadow zone is present.