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WIND TUNNEL STUDY AND NUMERICAL ANALYSIS ON PARTICULATE MATTER DISPERSION IN A THREE-DIMENSIONAL STREET CANYON
Restricted (Penn State Only)
Energy and Mineral Engineering
Master of Science
Date of Defense:
August 15, 2018
Jeremy Michael Gernand, Thesis Advisor
Particulate Matter Dispersion
Computational Fluid Dynamics
This study aims to identify lower risk exterior shelter areas and building air intake locations by modelling particulate matter (PM) dispersion in a three-dimensional street canyon from a point source and comprises a wind tunnel experiment and a computational fluid dynamics (CFD) simulation. The model street canyon for this investigation was a two-by-two building matrix of constant height with aspect ratios of 0.35, 0.70, and 1.05. A PM emission source external to the street canyon simulated a scenario of an accidental point release. The experimental PM source was simulated with water droplets from an ultrasonic humidifier in the wind tunnel. The wind tunnel experiment provided the data to calibrate the CFD simulation, from which a wider set of results could be evaluated. In the no-building case, measured PM concentrations from the wind tunnel experiment agreed with a modified Gaussian plume model of a continuous point source with a first-order decay term (adjusted R^2 = 0.786). The effective emission rate of the humidifier was estimated to be 5.27*106 particles/s. With street canyons, the association between a lower PM concentration and a greater aspect ratio contradicted past literature, mainly because the measurements locations were at the center of the internal intersection and the vertical vortices that could reduce street canyon ventilation capacity were absent in this experiment. The CFD simulation produced PM concentrations with a relative deviation of 54.9% on average from those of the wind tunnel experiment. Inside the street canyon, the leeward sidewalks of the transverse exits had the lowest PM concentration at the breathing level of 1.5 m above the ground. Regardless of wind direction, PM source location, and aspect ratio, the top 1 m of and the bottom 1 m of any façade surface and the roof had the lowest PM concentration among all building surfaces with access to the internal intersection. Therefore, if an accidental release of PM occurs and the source is identified as a point source outside the street canyons, pedestrians should move to the leeward sidewalks of the transverse exits, as other locations can have pedestrians exposed to at least a 60% higher PM concentration than the recommended evacuation site. For building construction and renovation, new ventilation air intakes should be installed at the top 1 m and the bottom 1 m of any façade surface and the roofs, as they registered up to 60.8% PM concentration at the unrecommended location in this scenario.
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