On the Effect of Regular Waves on Inclined Negatively Buoyant Jets

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.

2D PIV Measurement of Twin Buoyant Jets in Wavy Cross-Flow Environment

The multiport diffuser effluent discharge facilities constructed beneath the coastal waters were simplified in the laboratory as twin buoyant jets in a wavy cross-flow environment. The near-field flow structure of twin jets was studied by series of experiments conducted in a physical wave–current flume. The particle image velocimetry (PIV) system was used to measure the velocity field of the jets in various cross-flow-only and wavy cross-flow environments. By means of flow visualization, the distinctive “effluent cloud” (EC) phenomenon was clearly observed and the jet penetration height was found to be notably increased compared with that of cross-flow-only environment at the downstream position. It was found that the wave-to-current velocity ratio Rwc is a very important parameter for effluent discharge. A new characteristic velocity uch and the corresponding characteristic length scale lmb for twin buoyant jets in the wavy cross-flow environment were defined. Using curve-fitting, a new equation to estimate the effects of the jet-to-current velocity ratio (Rjc), wave-to-current velocity ratio (Rwc) and Strouhal number (St) on the jet trajectory were derived to enhance understanding the physical processes underpinning the rise and the dilution of buoyant jets, which is critical to the design of discharge facilities.

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.