CFD and wind-tunnel analysis of outdoor ventilation in a real compact heterogeneous urban area: Evaluation using “air delay”

Outdoor urban ventilation in a real complex urban area is investigated by introducing a new ventilation indicator – the “air delay”. Computational Fluid Dynamics (CFD) simulations are performed using the 3D steady Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) approaches. The up-to-date literature shows the lack of detailed evaluations of the two approaches for real compact urban areas. This study further presents a systematic evaluation of steady RANS and LES for the assessment of the ventilation conditions in a dense district in Nicosia, Cyprus. The ventilation conditions within the urban area are investigated by calculating the distribution of the age of air. To better assess the outdoor ventilation, a new indicator, the “air delay” is introduced as the difference between the local mean age of air at an urban area and that in an empty domain with the same computational settings, allowing the comparison of the results in different parts of the domain, without impact of the boundary conditions. CFD results are validated using wind-tunnel measurements of mean wind speed and turbulence intensity performed for the same urban area. The results show that LES can accurately predict the mean wind speed and turbulence intensity with the average deviations of about 6% and 14%, respectively, from the wind-tunnel measurements while for the steady RANS, these are 8% and 31%, respectively. The steady RANS simulations overestimate the local mean air delay. The deviation between the two approaches is 52% at pedestrian level (2 m)

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

CFD and wind-tunnel analysis of outdoor ventilation in a real compact heterogeneous urban area: Evaluation using “air delay”

Outdoor urban ventilation in a real complex urban area is investigated by introducing a new ventilation indicator – the “air delay”. Computational Fluid Dynamics (CFD) simulations are performed using the 3D steady Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) approaches. The up-to-date literature shows the lack of detailed evaluations of the two approaches for real compact urban areas. This study further presents a systematic evaluation of steady RANS and LES for the assessment of the ventilation conditions in a dense district in Nicosia, Cyprus. The ventilation conditions within the urban area are investigated by calculating the distribution of the age of air. To better assess the outdoor ventilation, a new indicator, the “air delay” is introduced as the difference between the local mean age of air at an urban area and that in an empty domain with the same computational settings, allowing the comparison of the results in different parts of the domain, without impact of the boundary conditions. CFD results are validated using wind-tunnel measurements of mean wind speed and turbulence intensity performed for the same urban area. The results show that LES can accurately predict the mean wind speed and turbulence intensity with the average deviations of about 6% and 14%, respectively, from the wind-tunnel measurements while for the steady RANS, these are 8% and 31%, respectively. The steady RANS simulations overestimate the local mean air delay. The deviation between the two approaches is 52% at pedestrian level (2 m).status: publishe

CFD and wind-tunnel analysis of outdoor ventilation in a real compact heterogeneous urban area: Evaluation using “air delay”

Outdoor urban ventilation in a real complex urban area is investigated by introducing a new ventilation indicator\u3cbr/\u3e– the “air delay”. Computational Fluid Dynamics (CFD) simulations are performed using the 3D steady\u3cbr/\u3eReynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) approaches. The up-to-date literature\u3cbr/\u3eshows the lack of detailed evaluations of the two approaches for real compact urban areas. This study\u3cbr/\u3efurther presents a systematic evaluation of steady RANS and LES for the assessment of the ventilation conditions\u3cbr/\u3ein a dense district in Nicosia, Cyprus. The ventilation conditions within the urban area are investigated by\u3cbr/\u3ecalculating the distribution of the age of air. To better assess the outdoor ventilation, a new indicator, the “air\u3cbr/\u3edelay” is introduced as the difference between the local mean age of air at an urban area and that in an empty\u3cbr/\u3edomain with the same computational settings, allowing the comparison of the results in different parts of the\u3cbr/\u3edomain, without impact of the boundary conditions. CFD results are validated using wind-tunnel measurements\u3cbr/\u3eof mean wind speed and turbulence intensity performed for the same urban area. The results show that LES can\u3cbr/\u3eaccurately predict the mean wind speed and turbulence intensity with the average deviations of about 6% and\u3cbr/\u3e14%, respectively, from the wind-tunnel measurements while for the steady RANS, these are 8% and 31%,\u3cbr/\u3erespectively. The steady RANS simulations overestimate the local mean air delay. The deviation between the two\u3cbr/\u3eapproaches is 52% at pedestrian level (2 m)