The aim of this thesis is modelling the phenomenon of dispersion of vehicular pollutants in deep and narrow streets, i.e. deep street canyons, as function of vehicular emissions and meteorological conditions. At present, the study of deep street canyons is not treated in exhaustive way. As a matter of fact, studies on roads with aspect ratio very close to one (AR ≈ 1) are more frequently reported. However the old historical centres of many cities, such as Naples, are characterized by narrow streets with AR > 1, which are often densely populated with, consequently, high vehicular flows and very high pollution levels. The study will carried out on a real street canyon in the historical centre of Naples, via Nardones. The choice has fallen just on this place for its geometric configuration that makes it almost an ideal street canyon and for its intensive traffic flow. In order to rich the aim of this thesis it will necessary to develop a CFD model able to predict, in a good way, the pollutant distribution inside the street canyon as function of meteorological data, background pollutant concentration, traffic intensity and pollution emissions. For the first thing we have to investigate on the ability of CFD software to model the dispersion mechanism of passive air pollution like CO in deep street canyon. To make this possible we must analyze its features in dealing with complex geometries like that of a deep street canyon and its surrounding area, the ability to deal with multi-specie gas mixture and turbulent flows. Obviously that should be done reaching a good accuracy and precision with a reasonably computational effort. So we need to define a geometrical model able to represent all the main features of the deep street canyon in a not complex way, to make an accurate but not enormous mesh and to choose a numerical algorithm and turbulence closure method accurate but not slow. After we had set up the model we need to obtain and analyse all the input data necessary, that is meteorological data like wind velocity and direction, traffic intensity and its time distribution, traffic pollutant emission rate and background pollutant concentration. We need also to analyze how all these input data affect the pollutant concentration level within the canyon and also find the most important ones i.e. those with biggest influence on canyon air quality. To make a good evaluation we must validated the model with measurements obtained in the situ. CFD models despite their accuracy and precision are a bit onerous, from the computational point of view, and difficult to set up so many empirical or semi empirical models were made up. These are faster than CFD models but are less accurate and usually are applicable to only a small range of cases because they are made up around those kinds of problems. Unfortunately almost all this empirical or semi empirical models were made up around regular street canyons so their application on a deep street canyon gives bad results, so we can use our CFD model to make changes to the parametric model in order to simulate the pollutant dispersion in deep street canyons.

MODELLAZIONE DELL’INQUINAMENTO ATMOSFERICO DI ORIGINE VEICOLARE IN DEEP STREET CANYON

MURENA, FABIO;D'ANNA, ANDREA;
2004

Abstract

The aim of this thesis is modelling the phenomenon of dispersion of vehicular pollutants in deep and narrow streets, i.e. deep street canyons, as function of vehicular emissions and meteorological conditions. At present, the study of deep street canyons is not treated in exhaustive way. As a matter of fact, studies on roads with aspect ratio very close to one (AR ≈ 1) are more frequently reported. However the old historical centres of many cities, such as Naples, are characterized by narrow streets with AR > 1, which are often densely populated with, consequently, high vehicular flows and very high pollution levels. The study will carried out on a real street canyon in the historical centre of Naples, via Nardones. The choice has fallen just on this place for its geometric configuration that makes it almost an ideal street canyon and for its intensive traffic flow. In order to rich the aim of this thesis it will necessary to develop a CFD model able to predict, in a good way, the pollutant distribution inside the street canyon as function of meteorological data, background pollutant concentration, traffic intensity and pollution emissions. For the first thing we have to investigate on the ability of CFD software to model the dispersion mechanism of passive air pollution like CO in deep street canyon. To make this possible we must analyze its features in dealing with complex geometries like that of a deep street canyon and its surrounding area, the ability to deal with multi-specie gas mixture and turbulent flows. Obviously that should be done reaching a good accuracy and precision with a reasonably computational effort. So we need to define a geometrical model able to represent all the main features of the deep street canyon in a not complex way, to make an accurate but not enormous mesh and to choose a numerical algorithm and turbulence closure method accurate but not slow. After we had set up the model we need to obtain and analyse all the input data necessary, that is meteorological data like wind velocity and direction, traffic intensity and its time distribution, traffic pollutant emission rate and background pollutant concentration. We need also to analyze how all these input data affect the pollutant concentration level within the canyon and also find the most important ones i.e. those with biggest influence on canyon air quality. To make a good evaluation we must validated the model with measurements obtained in the situ. CFD models despite their accuracy and precision are a bit onerous, from the computational point of view, and difficult to set up so many empirical or semi empirical models were made up. These are faster than CFD models but are less accurate and usually are applicable to only a small range of cases because they are made up around those kinds of problems. Unfortunately almost all this empirical or semi empirical models were made up around regular street canyons so their application on a deep street canyon gives bad results, so we can use our CFD model to make changes to the parametric model in order to simulate the pollutant dispersion in deep street canyons.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11588/7572
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact