Improving pedestrian micro-climate in urban canyons: City Center of Alexandria, Egypt

Abstract

Due to the accelerated pace of urbanization, the study of the local urban microclimate has acquired significance. A detailed and accurate prediction of outdoor ventilation and thermal comfort is required for a healthy environment, particularly in densely built areas, due to the complex interaction of physical phenomena across different length and time scales. Engineering approaches are critical for solving the issues of wind discomfort. These approaches can however not be applied independently of the architectural context. An interdisciplinary approach can bridge the gap between architectural design and engineering wind-comfort solutions in a coastal city of developing countries with a temperate climate. The current study aims to evaluate the effect of urbanization on an asymmetrical historical canyon in the city center of Alexandria, Egypt. Challenges and limitations are imposed regarding applying retrofitting techniques to improve pedestrian comfort without changing the historical features of these areas.This paper provides a Computational Fluid Dynamics (CFD) simulation of a residential district in the modern city of Alexandria which contains the library of Alexandria and the two oldest paved roads in the world which still in use until today. The 3D steady Reynolds-averaged Navier-Stokes (RANS) equations and the standard k-ε model are used to calculate the aerodynamic flow field. These computational settings were validated with previously published wind-tunnel results. The indices of thermal comfort were calculated using a Predicted Mean Vote (PMV) model utilizing Custom Field Functions (CFF). On-site measurements of air velocity, temperature, and humidity were conducted to validate the thermo-flow characteristics with the numerical simulation and they were in a good agreement.To reach the comfort level which contributes to a pedestrian-friendly environment, it brings a range of measures that covers qualitative design guidelines on street and building level to mitigate wind discomfort and excessive solar access in urban canyons. One of these measures presents (CFD) simulations for comparing the model of the modern city with a visualized model of the ancient city of Alexandria at the end of Cleopatra's reign. This comparison aims to give a close vision on how urbanization has influenced the aerodynamics and thermal comfort in this region. The current study helps urban planners and architects to enhance the current situation for better urban microclimate at the pedestrian level, without setting up new developments during hot summer days.