Research Of The Effect Of Jet Fan And Piston Wind On The Tunnel Natural Vents

of the urban tunnels, not only the critical concentration of various pollutants and the maximum allowed longitudinal ventilation velocity, but also to the emission concentration and total emissions of various pollutants in the natural vents and the tunnel portal should be considered from the perspective of environmental protection. Therefore, a ventilation shaft of multi-modular is widely adopted in multi-urban tunnels. The excessive use of mechanical exhaust tower always leads to discord with the local landscape because of its height. Moreover, the initial and running costs are always high. Setting natural vents at the top of the ventilation opening becomes a trend, but its designing parameters are not included in the current design code. Essential study on its feasibility is thus necessary.The combination of model experiment and numerical simulation is used to investigate the sewage effect when a small amount of natural air is set. Laboratory test is accomplished on the piston inside the wind tunnel, natural ventilation at the top of the tunnel, and the pressure regulator effect of jet fan. Furthermore, the effect of traffic flow, vehicle speed, and the location of natural ventilation openings on the discharge of pollutants inside the tunnel are also examined. The results show that the pollution discharge effect at the exit of the sewage achieves the best result under simple piston wind tunnel and the jet fans works efficiently on the voltage regulation for natural ventilation. Using Fluent software, three-dimensional physical model of the natural vents of urban transportation tunnel under piston wind only and both of piston wind and jet fans,are established. Based on the experimental results, a natural vent is set in the vicinity of tunnel exit, and the second one is in the different location. The exhaust volume of the two natural exhaust vents and the tunnel portal is tested and the pressure regulating effects are compared to provide a scientific calculating reference when can only be set in a fixed position a small amount of natural ventilation openings.