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 vehiclemounted 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.