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Show UNDERGRADUATE RESEARCH ABSTRACTS SPRING 200 Samuel Lefebvre Dickman Bhagirath Addepalli Reynolds Number Effects on Turbulent Transport in a Street Canyon Samuel Lefebvre Dickman (Bhagirath Addepalli, Eric R. Pardyjak) Department of Mechanical Engineering University of Utah Urban street canyon dispersion models are important if pedestrian air quality is to be predicted and considered in future building placement and ventilation plans. Many factors affect street level pollutant concentrations such as: traffic and vehicle characteristics, building height and spacing, boundary layer depth and mean free-stream velocity. Kastner-Klein et al. (2002) give experimental evidence for the relationship between mean wind speeds at building height and harmful pollutant concentrations such as nitrous oxides within a street canyon. An idealized street canyon was used to study the effect of Reynolds number (based on building height) on turbulent flow between buildings using Particle Image Velocimetry (PIV). The flow was simulated in a boundary-layer wind tunnel that utilized LEGO beds to simulate upstream urban roughness and two cubes separated to model a street canyon. A range of cube sizes (32 - 128 mm) were used to model buildings in an urban environment where the incident boundary-layer height was appreciably greater than the building height. The velocity data (see figure 1) were analyzed to describe the vortex pattern in the street canyon for different height and spacing configurations as well as to determine the Reynold's stress (see figure 2) and turbulent kinetic energy distribution. The data were analyzed further to determine the depth of turbulent penetration between the buildings. Maximum non-dimensional Reynold's stress and turbulent kinetic energy values were then plotted against Reynolds number to obtain regression data for urban street canyon situations. These data will be analyzed to correlate Oke's (1987) assertion that certain velocity flow regimes, namely skimming flows, promote pollutant concentration by inhibiting upward turbulent drafts. Eric R. Pardyjak |
