The wind effect on sound propagation over urban areas: Predictions for generic urban sections

The effect of a downward refracting atmosphere on distant sound propagation over various generic urban areas is predicted. The work uses a two-step approach, by first computing the wind field with computational fluid dynamics (RANS-CFD), and then adopting the mean wind field in a computational acoustics (PSTD-CA) method. These approaches were found to be valid for the studied geometries. For an urban configuration with multiple building blocks, a sound source is located in a street canyon, representing road traffic, and receivers are located at a distance up to 500 m. From results of calculations for various urban configurations, it can be concluded that: the sound levels increase due to the presence of a downward refracting atmosphere, and this effect is larger for higher frequencies; the wind effect ranges from 15 to 23 dB(A); the urban topology close to the source and receiver can largely influence the wind effect; whereas vegetated roofs have the potential to reduce sound levels without wind, in a downward refracting atmosphere the broadband effect is small (<2 dB(A)), however, a potential for reducing noise levels by roofs with low-frequency sound absorption has been identified.