Analysis on the Cross Pollution between Two Openings of the Long Tunnels on Lhasa-Rikaze Line

Among the diesel traction railway tunnels on Lhasa-Rikaze line of China, some of two tunnels are adjacent. When a train gets across a given tunnel, air pollutants extruded from the exit of the tunnel may diffuse towards the entrance of its neighboring tunnel and thus it results in thereof air pollution. The so-called cross pollution can affect the established ventilation scheme of excluding pollutants from the tunnels. Hence, in the present study, interactional influence of typical pollutant nitrogen dioxide in the long tunnel groups was concerned. The flow field and distribution of nitrogen dioxide concentration were considered to be transient. Three-dimensional computational fluid dynamics (CFD) models were established in the space between two tunnels using the state-of-the-art commercial CFD software package Fluent 6.2 and the models were validated. Cases of different distances L between two neighboring tunnel openings were studied and the effect of natural wind speed was also analyzed for the distributions of nitrogen dioxide concentration. It can be concluded that, both of short distance between two tunnel openings and side natural wind can lessen the cross pollution of two neighboring tunnels.