A Numerical and Experimental Study of Pollutant Dispersion in a Traffic Tunnel

Abstract

Three-dimensional turbulent flow and dispersion of gaseous pollutants carbon monoxide (CO) and nitrogen oxides (NOx) in a road tunnel was modeled using the standard k-epsilon turbulence model and solved numerically using the finite volume method. Vehicle emissions were estimated from the measured traffic flow rates and modeled as banded line sources along the tunnel floor. The effects of fan ventilation and piston effect of moving vehicles on the airflow and pollutant dilution were examined. The numerical results reveal that a peak velocity exists near the tunnel floor due to the piston effect of vehicles. The cross-sectional concentrations of air pollutants are non-uniformly distributed and concentrations rise with downstream distance. The piston effect of vehicles can alone provide 25%-34% dilution of air pollutants in the tunnel, compounded 43%-70% dilution effect according to the ventilation condition.

Computational study of effects of jet fans on the ventilation of a highway curved tunnel

“…The research on the comparison of flow performance in a pipe with three different RANS models, namely k-e, k-x, Reynolds stress models (RSM), is found that the simulation results among the three models in the mean velocity profile and the friction factor match quite well with the experimental results and RSM consumes more time though it can give some additional information on the shear stress correlations (Vijiapurapu and Cui, 2010). Furthermore, the standard k-e turbulent model has the advantage of being extensively used in simulation of tunnel ventilation and has been validated against the experimental data (Chung and Chung, 2007;Vega et al, 2008;Solazzo et al, 2008;Huang et al, 2008). Accordingly, the standard k-e turbulent model due to Launder and Spalding (Launder and Spalding, 1974) was adopted in this research.…”

“…The outflow boundary condition is used at the tunnel outlet, namely @U=@n ¼ 0 (where U = u, k or e). The fans inlet also adopts the outflow boundary condition (Chung and Chung, 2007). The jet fans velocity U j = 33 m/s is specified for the fan outlet according to the actual design data.…”

“…The air quality in a road tunnel would easily deteriorate if the exhaust gas emitted from the vehicles is not promptly removed, because the road tunnel is normally enclosed or partially enclosed (Chung and Chung, 2007). As a result, effective ventilation in a road tunnel is extremely important to prevent the harmful substances from affecting tunnel users and to maintain good visibility in tunnels.…”

“…As a result, effective ventilation in a road tunnel is extremely important to prevent the harmful substances from affecting tunnel users and to maintain good visibility in tunnels. In long vehicle tunnels, mechanical ventilation systems are often employed to keep the amount of toxic gases below safety limits (Chung and Chung, 2007;Chen et al, 1998;Chow and Chan, 2003;Bari and Naser, 2005). Such systems are classified into longitudinal ventilation, transverse ventilation, semi-transverse ventilation and combinations of them.…”

“…The researches above mainly focus on the experimental study and many numerical studies have also recently been conducted. Chung and Chung (2007) carried out a numerical simulation to study effects of jet fans and moving vehicles on the flow field and the dispersion of gaseous pollutants in a road tunnel. The results showed that the pollutants concentration increased with the increase of downstream distance due to the effect of jet fans.…”