Numerical simulation of pollutant dispersion in urban roadway tunnels

Abstract

Vehicular toxic emissions can easily contaminate the air quality of the enclosed tunnel environment, especially during rush hours with traffic jam events or low vehicle speeds, which poses serious health hazards to road utilizers. The piston effect generated by moving vehicles was normally considered adequate to discharge vitiated air out of short tunnel based on a typical driving speed. However, complex traffic conditions may yield unexpected consequences on in-tunnel air quality levels. This study numerically investigated the CO 2 concentration to identify the in-tunnel pollutant dispersion under three traffic conditions including severe traffic congestion and traffic flow with low vehicle speeds. Fan conditions were considered to model the influence of mechanical winds on pollutant dispersion and comparison with vehicular piston effect was also performed. The results revealed elevated pollutant concentration regions were found at the vicinity of near-ground region and tunnel downstream. The vehicular piston effect can sufficiently remove the in-tunnel vehicular emissions when vehicles travel at relatively higher speed. However, pollutant accumulation occurs when vehicles are idling or moving at slow speed. Compared with traffic piston effect at high travelling speed, the mechanical ventilation of ceiling mounted fans only generate a limited contribution to the removal of emissions.

Carbon Monoxide and Particulate Matter Concentrations inside the Road Tunnels of Guanajuato City, Mexico

“…As can be seen in Fig. 6, corresponding to the BA tunnel, the vehicular congestion with low vehicular flow concurs with the maximums of pollutant concentrations (PM2.5 and PM10) observed at 300, 400 and 650 meters, approximately (Dong et al, 2017). On the other hand, a progressive increase of the PM2.5 and PM10 concentration is generated with the vehicular flow and wind speed from the entrance to the exit of LA and GA tunnels showing the absence of vehicular congestion inside the tunnels.…”

“…13 stagnation of the pollutants due to the low wind speed because the vehicles are forced to stop and drive at a very low speed, diminishing the piston effect that pushes the pollutant outside the tunnel (Dong et al, 2017).…”

“…As can be seen in Fig. 6, the variation of the concentration of CO inside the tunnels is directly related to the number of vehicles entering them and to the variations in the wind speed that generates turbulence of the toxic gases towards the exit of the tunnels (Brimblecombe et al, 2015;Dong et al, 2017). During the monitoring on Tuesday, 131 vehicles entered in the 30 minutes during the monitoring time from the entrance to exit of LA tunnel, 203 vehicles traveled through the BA tunnel in 32 minutes and 182 vehicles went through the GA tunnel in 35 minutes during the monitoring time.…”

A large eddy simulation of the dispersion of traffic emissions by moving vehicles at an intersection

“…This parametrization was used within a Reynolds averaged Computational Fluid Mechanics (CFD) simulation by Thaker and Gokhale (2016), however this approach does not resolve the temporal variation in concentrations and magnitude of high concentration peaks seen in field study measurements. Other Reynolds averaged simulations using a moving mesh were undertaken by Kim et al (2016) and Dong et al (2017). A Large Eddy Simulation (LES) approach was used by Zhang et al (2017), where each vehicle's drag force was applied to the air using a momentum source term.…”

Numerical Investigation of The Aerodynamics of Lorry Platooning Travelling through Road Tunnels

“…However, LES requires vast computational resources, especially for high Re number flow [60]. On the other hand, Reynolds Averaged Navier-Stokes (RANS) is more widely used to simulate vehicle aerodynamics [46,[61][62][63][64], because it has a lower requirement for mesh density than LES. The present study adopts Improved Delayed Detached Eddy Simulations (IDDES).…”