Showing papers by "Silvana Di Sabatino published in 2014"

Validation of temperature-perturbation and CFD-based modelling for the prediction of the thermal urban environment: the Lecce (IT) case study

Abstract: This paper discusses the performance of the temperature perturbation-type ADMS-Temperature and Humidity Model (ADMS-TH) and the Computational Fluid Dynamics (CFD)-based model ENVI-met for the prediction of urban air temperature using measurements collected in the city of Lecce (IT) in summer 2012. The goal is to identify the most important factors influencing numerical predictions. Direct comparisons with measured data and statistical indices show that modelled results are within the range of acceptance. Daily trends are well captured although an underestimation of maximum temperature is observed. In ADMS-TH this is due to an underestimation of sensible heat fluxes during daytime, while in ENVI-met it can be attributed to an underestimation of turbulent momentum and thermal diffusivity. Overall, ADMS-TH did predict the temperature cycle with higher accuracy than ENVI-met and its performance was particularly good during the night. ENVI-met required an ad-hoc tuning of surface boundary conditions to predict nocturnal cooling, satisfactorily.

Study of the urban heat island in Lecce (Italy) by means of ADMS and ENVI-MET

Abstract: The urban heat island (UHI) phenomenon may produce several cascade effects on citizens’ health, energy consumption and air quality. Numerical modelling is recognised to be a powerful tool for the analysis of the UHI, although the question of which model to use (as implied in the ‘fit-for-purpose’ approach) much depends on the application and on the result of satisfactory validation against field measurements. In this paper, two different modelling approaches are applied, namely the integral-semi-Gaussian model ADMS-TH and the CFD-based model ENVI-met, to assess the UHI phenomenon in a city of south Italy (Lecce). Modelling results are validated against field measurements collected during summer 2012. The results suggest that the integral model has the ability of capturing the UHI cycle at city scale, while CFD modelling did not provide any substantial improvements in terms of local geometric effects on temperature distribution.

The Effects of Trees on Micrometeorology in a Medium-Size Mediterranean City: In Situ Experiments and Numerical Simulations

Abstract: This study analyses the aerodynamic effects of trees on local meteorological variables through in situ measurements and Computational Fluid Dynamics (CFD) simulations. Measurements are taken in the inner core of a medium-size Mediterranean city (Lecce, IT) where two adjacent street canyons of aspect ratio H/W∼1 (where H is the average building height and W is the average width of the street) with and without trees are investigated. Building facades and ground temperatures are estimated from infrared (IR) images, while flow and turbulence are measured through three ultrasonic anemometers placed at different heights close to a building facade at half length of the canyon. Tree crown porosity is evaluated through the Leaf Area Index (LAI) measured by a ceptometer. Numerical simulations are made using a CFD code equipped with the Reynolds Stress Model (RSM) for the treatment of turbulence. Overall, the analysis of measurements shows that trees considerably reduce the longitudinal wind speed up to 30%. Trees alter the typical diurnal cycle of surface and air temperature within the canyon, suggesting that in nocturnal hours the trapping of heat is more important than the power of passive cooling through evapo-transpiration. Comparative numerical simulations provide further evidence that flow velocity reduces in presence of trees and although the typical wind channeling observed without trees is still maintained, trees enhance the formation of a corner vortex leading to reverse flow at the openings of the street. The reduction of the exchange of momentum between the canyon and the atmosphere above, shown by the measurements in presence of trees is confirmed by numerical simulations.Copyright © 2014 by ASME