Keywords: atmospheric pollution, building, dispersion, near-wake recirculation, peak-to-mean, concentration ratios, plume, air pollution, air quality, horseshoe vortex
Plume dispersion in the wake of a rectangular model building
A field experiment was specifically designed and conducted to investigate the width of the near-wake recirculation region of a wide and slender model building. Tracer gas was released from the centre of the leeward side of the building. The results suggested that the width of the wake ranged between 0.6 and 1.1 W in the case of the wind normal to the short side and between 0.5 and 0.9 W in the case of the wind normal to the long side of the building. The length of the near-wake recirculation region was also calculated using a simple empirical expression. Both results are in agreement with flow visualisation trials conducted around the same building. Further experiments showed that in the near-wake region higher rates of dispersion occurred, together with increased residence of the pollutant and that the plume in the wake of the building was to some extent bifurcated, due to the effect of the horseshoe vortex.