A Model for the Far-Field Anisotropic Acoustic Emission of Rotating Turbulence

Abstract

The isotropy of homogeneous turbulence can be broken in flows subject to background rotation. This results in the anisotropic structuration, with large-scale vortices elongated along the rotation axis, and inertial waves with anisotropic mixing properties. Considered as acoustic sources, these anisotropic structures produce noise with characteristics different from the acoustic emission of isotropic turbulence. We propose a computationally efficient model that helps to assess these differences, and to quantify the properties of noise produced by anisotropic turbulence. The simplified configuration is homogeneous turbulence submitted to rotation, for which we evaluate the far-field acoustic emission. A combination of two models is used: Lighthill’s acoustic analogy, for the computation of far-field sound emission, and Kinematic Simulation, a stochastic model for homogeneous turbulence, adapted for rotation. The sound spectrum dependence on the rotation rate and the directivity of acoustic intensity are studied and shown to differ from an isotropic emission.