Numerical investigation of airflow patterns and pollutant dispersions induced by a fleet of vehicles inside road tunnels using dynamic mesh part Ⅰ: Traffic wind evaluation

摘要

The transient piston effect induced by a fleet of vehicles that passes through a tunnel can dominate pollutant dispersion, human exposure, and tunnel ventilation. This study employed the realizable k-epsilon model together with the dynamic mesh technique to analyze the characteristics of the transient traffic piston effect inside a tunnel. A tunnel model with a length of 450 m and a 450-m extension from the outlet in the driveway direction was developed, which contained 36 gasoline-powered cars located in nine rows with four vehicles per row. The unsteady three-dimensional model was validated by comparing the simulation results with the field-measurement data of a real tunnel. The simulation results show that traffic wind was significant, and is sufficient for diluting the pollution inside the tunnel if the vehicle speed is over 20 km/h. The peak-to-valley ratio of traffic-wind velocity below 60 km/h in three specific planes (Z = 0.5 m, Z = 1.5 m, and the tunnel outlet) was in the range of 1.47-1.77, which was slower than the 40-km/h (2.00-2.36) and 20-km/h (2.45-3.09) cases. Ventilation fans should be added to ensure fresh air supply as well as human health and safety when the vehicle speed is not faster than 40 km/h. A drag coefficient of 0.1-0.3 should be used to increase the accuracy of the pressure analysis if a fleet of vehicles moves inside the tunnel at a speed of not less than 40 km/h.