Abstract
We experimentally investigated the impact of rooftop stack position on the pollutant entrapment within 2D street canyon configurations. Analyses were performed in a water channel loop system by using the image analysis techniques: FTV (Feature Tracking Velocimetry) and LIF (Light Induced Fluorescein) respectively for measuring velocity and concentration. The set-up consists in an array of 20 identical buildings with aspect ratio equal to one (ARB = B/H, where H is the height of the eaves and B is the building width), mimicking an idealized 2D urban canopy. They were equally spaced with a unitary canyon aspect ratio (defined as ARC = W/H; where W is the distance between buildings facades), and varied in shape by using flat and gable roofs with pitch α = 45°, with different chimney positions and heights, for a total number of 9 investigated configurations. Results demonstrate that the presence of gable roof significantly varies the flow in the shear layer, which, in combination with different chimney position and height, lead to not trivial effects on pollutants dispersion.
Highlights
We experimentally investigated the impact of rooftop stack position on the pollutant entrapment within 2D street canyon configurations
They were spaced with a unitary canyon aspect ratio, and varied in shape by using flat and gable roofs with pitch α = 45°, with different chimney positions and heights, for a total number of 9 investigated configurations
The urban canopy is characterized by a complex geometry that interacts with the fragile equilibrium governing atmosphere, soil and subsoil system
Summary
The urban canopy is characterized by a complex geometry that interacts with the fragile equilibrium governing atmosphere, soil and subsoil system. Saathoff et al (2009) investigated in a wind tunnel model the roof key role in near field dispersion, in case of a rooftop stack located downwind a single building They varied building heights, rooftop structure and wind directions and compared results with ASHRAE models, pointing out their weakness in some of the adopted configurations. The plume behavior is affected by many factors, apart from the surrounding area, the plume buoyancy and the atmospheric conditions In their pioneering work, Willis and Deardorff (1983) showed how a stack emission evolves in case of a Convective Boundary Layer, a situation where more complex spatial structures in case of flat terrain (Badas and Querzoli 2011). Results show the complex interaction between the plume and the underlying urban canyon, which may lead to unexpected results in terms of canyon pollution
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