Pollutant dispersion in a group of courtyard buildings

As stated by the World Health Organization (WHO), the air pollution in the urban environment is the silent cause for around seven million death worldwide. This is due to the indoor and outdoor exposure to various pollutants emitted in the built environment: as the global trend is an increase of the population living in towns, this issue is predicted to become even worser. As a matter of fact, the built environment can cause the trapping of pollutants instead of their dispersion. In this work, the dispersion of a plume of a pollutant (carbon monoxide, CO), emitted from a chimneystack above the roof of courtyard in a group of courtyards, is investigated. This is achieved employing the ENVI-met software, able to model, among the others, the turbulence and pollutant dispersion in the built environment. Results show, among the others, how the pollutant emitted from an upstream building can harm also the downstream buildings.

On The Effect Of The Shape Of Buildings And Chimneystacks On Ventilation And Pollutant Dispersion

The purpose of this work is to investigate the modifications induced by the change of the roof shape in the flow field, inside and above the buildings, with an attention to their capability to modify the air quality and the dispersion of pollutants released from chimneystacks. We have carried out laboratory experiments on arrays of identical buildings, with symmetrical dual-pitched or flat roofs, and chimneystacks of different heights and positions. The experiments have been carried out in a close-loop water-channel, where two non-intrusive and quasi-continuous in space Digital Image Analysis technique have been implied to measure the velocity fields (Feature Tracking Velocimetry) and the concentration fields (Laser Induced Visualization). Results have highlight the meaningful role of gabled roofs in modifying turbulence, which increases the air exchange rate between the street canyon and the outer flow, but, in some conditions, they increase the dragging of pollutant inside the canyon. These results can have an immediate practical impact on the building design and on planning strategies, as the roof shape can be a useful tool to enhance natural ventilation and pollutant, humidity and/or heat dispersion, i.e. the air quality in urban and industrial areas.

An Investigation on the Effects of Different Stratifications on Negatively Buoyant Jets

Negatively buoyant jets develop when fluids are released upwards into a lighter fluid or, vice versa, downwards into a heavier fluid. There are many engineering applications, such as the discharge, via submerged outfalls, of brine from desalination plants into the sea. Some concerns are raised about the potential negative environmental impacts of this discharge. The increase in salinity is the major cause for environmental impact, as it is very harmful to many marine species. The diffusers for brine discharge are typically inclined upwards, to increase the path before the brine reaches the sea bottom, as it tends to fall downwards driven by negative buoyancy. The negatively buoyant jet that develops conserves axisymmetry only when released vertically, so that it is not possible to use the well-known equations for axisymmetric jets. The main target of this paper is to investigate on a laboratory model the effects of different stratifications on the features of negatively buoyant jets. This has been done via a LIF (Light Induced Fluorescence) technique, testing various release angles on the horizontal and densimetric Froude numbers. Except for the initial stage, a different widening rate for the upper boundary and the lower boundary has been highlighted.