Aircraft induced sound propagation in the urban context

Abstract

Exposure to excessive community noise has become a large environmental health concern. Noise pollution continues to increase while it is accompanied by direct, as well as cumulative adverse health effects. In addition, prolonged exposure to excessive noise levels also has a negative economic impact. The incorporation of numerical tools in the design process could counter this problem. However, traditional models are not widely available or often simplified. This illustrates the complexity of the matter, as noise is influenced by a variety of acoustic propagation effects. Moreover, the focus is predominantly on noise from railways and roads or for indoor settings. Little information is available about the dispersion of sound around buildings emitted by overhead sound sources, i.e. aircraft. This means that most numerical models neglect or simplify meteorological effects, which may result in misinterpretation of the urban noise situation. This graduation thesis addresses the question whether the design of the build environment can yield a reduction in aircraft induced noise, including the presence of a downward refracting atmosphere. The outcome may assist architects and urban designers to improve the soundscape quality in areas affected by aircraft noise. Due to the Covid-19 pandemic, the application of a self-made low turbulence wind tunnel is explored to perform scale model measurements that could be extended towards a full-size experiment in future studies. The wind tunnel was able to generate a uniform velocity profile which was suited to be used in this experiment. However, limitations were observed considering higher order wind tunnel reflections and masking of sound by the fan. In addition, a CFD study was performed to get insights into the interference between geometric configurations and flow patterns inside the wind tunnel. The building geometry influences the sound pressure level near the façade without a line of sight towards the sound source. The differences between the geometries studied in this thesis increased for decreasing grazing angles. The results also suggest the independency of canyon width on the shielding performance in case of treated canyon facades (covered with sound absorbing material), obstructed sound paths and absence of wind. In the presence of wind, sound pressure levels were further reduced for smaller treated canyons. Moreover, the results demonstrate a strong downward refracting atmospheric effect which increases the sound pressure levels inside shielded canyons. Flat roofs reduce wind effects which means that the effects of a downward refracting atmosphere are less intense compared more common typologies containing e.g. gabled roof tops.