| In recent decades the world has seen a rapid growth of population in urban areas, thus necessitating increased emphasis on quality of life and security of urban dwellers. Central to environmental issues is the quality of air, which is largely determined by meteorology and pollutant sources within and around urban canopies. The main goal of the study reported herein is to improve fundamental understanding of mean flow and turbulence within urban canopies using theoretical, laboratory and field experimental work spanning a variety of scales. The measurements of the Mock Urban Setting Test (MUST) field campaign, conducted in an instrumented mock building cluster, were used to investigate vortex shedding, spatial flow adjustment, flow patterns and turbulence within an idealized but a man-sized building canopy. New scaling laws were developed for the canopy velocity based on the approach flow parameters and canopy morphology, which was found to perform better than existing velocity scales. The flow adjustment at the leading and trailing edges of the MUST canopy was found to be in good agreement with a distributed force model. Different flow patterns close to the street level of MUST and Joint Urban 2003 (JU 2003) campaigns were identified for different approach flow directions, and a detailed study of flow patterns was performed for the case of (dominant) normal incoming winds. Observed flow patterns were compared with those expected based on previous laboratory and numerical studies conducted with idealized building configurations, and the agreement was encouraging. New laboratory experiments were also conducted on flow and turbulence around single obstacles of the same shape and aspect ratio as that of MUST, and the results were used to investigate scalability of small-scale low Reynolds number experimental results to real flows. Comparisons showed a good agreement for the streamwise component, except in the upper part of the canyon. The experiments were extended to include varying streamwise separation between buildings, corresponding to wake interference and skimming flow regimes. Significant changes to the profiles shapes of mean flow and turbulence were noted inside the canyon and immediately above. |
