Turbulence and Air Exchange in a Two-Dimensional Urban Street Canyon Between Gable Roof Buildings

摘要: We experimentally investigate the effect of a typical building covering: gable roof, on flow and air exchange in urban canyons. In general, morphology canopy is very varied complex, depending large number factors, such as arrangement, or terrain. Therefore we focus simple, prototypal shape, two-dimensional canyon, with aim elucidating some fundamental phenomena driving street-canyon ventilation. Experiments are performed water channel, over an array identical prismatic obstacles representing idealized canopy. The aspect ratio, i.e. canyon-width to building-height ranges from 1 6. Gable roof buildings 1:1 pitch compared flat roofed buildings. Velocity measured using particle-image-velocimetry technique dynamics discussed terms mean second- third-order statistical moments velocity. ventilation interpreted by means simple well-mixed box model outflow rate residence time computed. Results show that roofs tend delay transition skimming-flow wake-interference regime promote development deeper more turbulent roughness layer. presence significantly increases momentum flux, especially for high packing density. improved buildings, beneficial significant narrow Accordingly, unit ratio reduce factor 0.37 roofs, whereas decrease only 0.9 at largest ratio. Data analysis indicates that, 30% when decreased 6 2, this parameter weakly dependent case roofs.