For individuals who live in urban areas, rising temperatures translate to increased heat stress when outdoors. To develop strategies for reducing these unwanted effects, civil and environmental engineers require a greater understanding of the fluid dynamics of air flow within urban streets and the overall urban space. We experimentally investigated how air flow within urban streets is shaped under different influences. Considered that the natural synoptic wind above streets, which acts as an inertial forcing, as well as the different heating of buildings and walls under direct solar radiation, which promotes a buoyancy-driven flow. The breathability determines the capacity of a street or city to remove heat, pollution, and moisture produced from the human activities within, and therefore determines the comfort level and risk of mortality for citizens.
The study used a water channel apparatus that contained scaled-down physical models of an idealized symmetric urban canyon. A particle image velocimetry system measured the time-resolved flow velocity field. Three model street-canyon cavities were examined with varying height-to-width (aspect) ratios. We found that the two forcing influences combine to manifest a resulting air flow pattern which may completely differ depending on how narrow or wide the street is compared to the height of the surrounding buildings.In some cases, the fluid dynamics condemns the air to a double recirculating pattern, thus suppressing severely the breathability capacity. For those situations, local actions within the street, such as planting trees, are the only refuge.
The Project EXCELLENCE//1216/0294 is co-financed by the European Regional Development Fund and the Republic of Cyprus through the Research and Innovation Foundation
