Identification of pedestrian-level ventilation corridors in downtown Beijing using large-eddy simulations

Ventilation corridor, which is defined as air path that is composed of urban open spaces with low aerodynamic roughness and airflow resistance, has been discussed in Beijing previously. This study links up with different scales of ventilation characteristics in Beijing using multi-scale numerical simulations. Validated Weather Research and Forecasting simulations demonstrate the spatial wind patterns in two seasons and the impact of urban roughness on wind speed. Combined with a Lagrangian backward trajectory model, boundary layer ventilation corridors of Beijing are identified. To provide more fundamental and precise supporting information to tackle the complexity of ventilation environment in the capital city, a set of building-resolved large-eddy simulations (LES) was conducted. Each simulation covers a neighbourhood of 3 km by 3 km and the combined model domain covers the major part of downtown Beijing. Urban canopy ventilation and the influences of urban parameters are investigated. A multiple linear regression model between site-averaged velocity ratios and morphological parameters including building coverage ratio, frontal area index, and building volume is established to identify the importance of different urban factors. Open spaces in urban areas play an important role in urban ventilation. Pedestrian-level ventilation corridors are identified by combining all LES-computed velocity ratios in downtown Beijing. For both annual prevailing (South-south-west) and winter prevailing (North-northwest) winds, three pedestrian-level ventilation corridors were identified. Land use on the upstream and along these corridors should be protected for climatic and environmental enhancement.