Influence of street obstructions on flow processes within urban canyons

This paper is concerned with modelling of the motion of air within the urban environment and is directed towards a deeper understanding and controlling of pollutant dispersion in individual street canyons. Some possible methodologies by which the roughness associated with obstacles, such as small buildings, kiosks, trees and stationary vehicles within the canyon may be described for incorporation into an overall canyon model, are discussed. This is illustrated by results from a simple wind tunnel experiment utilising an idealised two-dimensional street canyon in which the internal roughness is represented by an array of vertical cylinders. These reveal the presence of complex flow patterns within the roughness layer. Integrated and averaged mean velocity and turbulence intensity parameters are presented to indicate the extent of the effect of the presence of the internal roughness upon the canyon flow regime.