Wind field characteristics over the negative terrain for Loess Tableland valley town under stable background wind

Abstract

Urban ventilation is an effective means of improving air quality and promoting sustainable development of urban areas. For Loess Tableland valley towns dependent on heavy industry, the ventilation characteristics of the town area are poorly understood. Therefore, it is important to first explore wind field characteristics over the negative terrain. In this study, the wind field over the negative terrain under the stable background wind was investigated by orthogonal experiments. Simulation results show that airflow patterns in the valley space can be classified into five categories, which are the unstructured flow, combination of unstructured flow and circulation organization, circulation organization, combination of circulation organization and background wind and background wind. The airflow pattern can affect significantly the vertical distribution of the velocity, temperature and air age in the valley space, and thus affecting the ventilation performance of the valley towns. Ventilation performance of valley towns was worse under the unstructured flow conditions, while it was optimal under the background wind conditions. Additionally, sensitivities of terrain factors influencing ventilation evaluation indices at the pedestrian level were analysed. The present study has provided a scientific basis for town planning and industrial emissions in the valley towns.