Calculations of low-frequency wind noise along a low two-dimensional hill surface

Abstract

Measurement of outdoor sound propagation is often limited by wind noise, i.e. pressure fluctuations from atmospheric turbulence, especially for infrasound and low audible frequencies. Over a flat ground surface, the spectral density of wind noise can be predicted by the shear-turbulence mechanism for static pressure fluctuations using a mirror flow atmospheric turbulence model for the inhomogeneous surface-blocking effect. This study moves beyond a flat ground model to consider the effects of flow distortion by weak topography on surface wind noise, specifically, flow over a low two-dimensional hill, free from separation, at large Froude number. The integral solution for the pressure Poisson equation is used as a starting point, with turbulence modeled by the mirror flow in surface-following coordinates. The perturbation analysis of Hunt et al. [Q. J. R. Meteorol. Soc. 114(484), 1435–1470 (1988)] is used to model the mean shear rate as a function of elevation and distance over the hill. For upwind, downwi...