Full-scale experiment on the ventilation performance of vehicle-mounted mobile fans in a road tunnel

The aim of this study is to investigate the effects of different arrangements and parameters of vehicle-mounted mobile fans on ventilation effectiveness in road tunnels. The Coanda effect is a phenomenon in fluid dynamics where a fluid (liquid or gas) tends to adhere to a curved surface rather than follow a straight path. In other words, the jet adheres to the tunnel ceiling, and this tendency can be counteracted by deflecting the fans. Through a series of full-scale tunnel experiments, the effects of different pitch angles and arrangement spacing of vehicle-mounted mobile fans on the airflow characteristic and ventilation performance in road tunnels were investigated. The experiments revealed that larger pitch angles on vehicle-mounted mobile fans lead to shorter distances for airflow development. When two vehicle-mounted mobile fans are positioned at intervals of 60 m or 90 m, the development distance of the airflow is 60 m. The wind flow decreases rapidly within 200 m in front of the fan outlet. Additonally, while a single vehicle-mounted mobile fan is in operation, the stabilized air velocity is about 2 m/s. The airflow stabilizes at a velocity of 3.8 m/s when two vehicle-mounted mobile fans work in tandem. The ventilation efficiency of the vehicle-mounted mobile fans is higher than 70 %. The research findings, derived from full-scale experiments, serve as a robust foundation for the effective utilization of vehicle-mounted mobile fans in real tunnel fire scenarios and offer practical guidance for tunnel safety management and emergency response.