Exploring airflow patterns at the roof parapet of a building

Roof parapet structures can affect airflow patterns and outdoor wind field on rooftops, potentially leading to pollutant accumulation and indoor infiltration. This study is to clarify the airflow patterns on the rooftop with a parapet and the thermal effect on the indoor environment. In this study, various factors that influence airflow characteristics on rooftops with parapet structures were investigated through numerical simulation. The findings showed that when the wind angle is 0°, the recirculation zone on the rooftop is the largest. In addition, when heights of parapets are 0.6 m and the Richardson number ( Ri) is less than 2.5, an obvious vortex core can be observed at the top. When Ri > 13.34, a complete recirculation zone cannot be observed, but when increasing the height of the parapet, a vortex area can be observed on the roof under the condition of a high Ri. Moreover, this study examined the impact of the building height (including parapet), width and proportion of the parapet height to the building height on the size of the recirculation zone on the rooftop. The study recommends the use of a scaling coefficient R* to evaluate the size of the recirculation zone on the rooftop.