Numerical and wind-tunnel evaluation of ventilation conditions in a real compact heterogeneous urban area

Given the rapid increase of urbanization and urban population worldwide, the urban air quality, wind and thermal comfort have become increasingly important matters. In this perspective, accurate prediction of the ventilation conditions in complex urban areas is of significant importance. CFD has been used in different occasions in the past to investigate the pedestrian-level wind conditions in urban areas. The 3D steady Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulations (LES) approach have been widely used. However, a detailed evaluation of the two approaches for this application has not yet been performed. This paper presents a systematic evaluation of 3D steady RANS and LES CFD simulations of wind flow in a compact heterogeneous urban area in the city of Nicosia, Cyprus. The ventilation conditions are investigated by assessing the distribution of the age of air at pedestrian height. The evaluation is based on validation with wind-tunnel measurements of mean wind speed and turbulence intensity for the same urban area, performed in an atmospheric boundary layer wind-tunnel at scale 1:250. The results show that the average deviations of the obtained results by steady RANS and LES with the experiments are about 10% and 7.3% for the mean wind speed. For turbulence intensity, this deviation is 42% and 20%, respectively.