A numerical investigation into the performance of two types of jet fans in ventilation of an urban tunnel under traffic jam condition

Abstract

Recent increase in construction of road tunnels in cities, has increased the need for effective ventilation for removing toxic gases emitted by vehicles from the tunnels especially during traffic jams. Severe traffic jam is an inevitable part of the urban life. The objective of this study is to investigate the ventilation effectiveness of the Banana® jet fan and the traditional straight jet fan and also to compare their performance in exhausting the vehicle emissions in severe traffic condition from the tunnel. The effects of adverse wind blowing into the tunnel outlet portal and the impact of mountain blocks, located at the tunnel inlet and outlet, on the airflow field are also investigated. The standard k–ε turbulence model was used in the computational fluid dynamic (CFD) analysis to simulate the ventilation airflow in a 919m tunnel. For severe congested traffic condition, the simulation results show that the tunnel airflow rate induced by Banana® and traditional jet fans is roughly the same. This leads to an almost similar average of Carbon Monoxide (CO) concentration at the tunnel exit. The performance of the Banana® jet fans, however, is more desirable regarding the local concentration of CO near the human breathing zone of the tunnel. Moreover, it is shown that the effect of adverse wind in decreasing the tunnel airflow rate predicted by the present simulations is much stronger compared with that suggested by the current engineering design approach.