Sonic boom reflection over urban areas

Sonic boom propagation over urban areas is studied using numerical simulations based on the Euler equations. Two boom waves are examined: a classical N-wave and a low-boom wave. Ten urban geometries, generated from the local climate zone classification [Stewart and Oke (2012), Bull. Am. Meteorol. Soc. 93(12), 1879-1900], are considered representative of urban forms. They are sorted into two classes, according to the aspect ratio of urban canyons. For compact geometries with a large aspect ratio, the noise levels and the peak pressure, especially for the N-wave, are highly variable between canyons. For open geometries with a small aspect ratio, these parameters present the same evolution in each urban canyon, corresponding to that obtained for isolated buildings. A statistical analysis of the noise levels in urban canyons is then performed. For both boom waves, the median of the perceived noise levels mostly differs by less than 1 dB from the value obtained for flat ground. The range of variation is greater for open geometries than for compact ones. Finally, low-frequency oscillations, associated with resonant modes of the canyons, are present for both compact and open geometries. Their amplitude, frequency and decay rate vary greatly from one canyon to another. (C) 2022 Author(s)

Automated summary

This study investigates the propagation of sonic booms over urban areas through numerical simulations based on the Euler equations. Two types of boom waves, namely the classical N-wave and the low-boom wave, are examined. Ten urban geometries, generated based on the local climate zone classification, are considered representative of urban forms. The study finds that the aspect ratio of urban canyons significantly affects the noise levels and peak pressure, especially for the N-wave, with compact geometries exhibiting higher variability between canyons. Open geometries, on the other hand, show similar parameter evolution to isolated buildings. A statistical analysis of noise levels in urban canyons reveals that the median perceived noise levels differ by less than 1 dB from that of flat ground, with greater variations observed in open geometries compared to compact ones. Additionally, low-frequency oscillations associated with resonant modes of the canyons are observed, with significant variations in amplitude, frequency, and decay rate among different canyons.