Measurement and Three-Dimensional Modeling of Airflow and Pollutant Dispersion in an Undersea Traffic Tunnel

Abstract

Airflow and pollutant dispersion in a cross-harbor traffic tunnel were experimentally and numerically studied. Concentrations of the gaseous pollutants CO, NO x , and total hydrocarbons (THC) at three axial locations in the tunnel, together with traffic flow rate, traffic speed, and types of vehicle were measured. Three-dimensional (3D) turbulent flow and dispersion of air pollutants in the tunnel were modeled and solved numerically using the finite volume method. Traffic emissions were modeled accordingly as banded line sources along the tunnel floor. The results reveal that cross-sectional concentrations are nonuniformly distributed and that concentrations rise with downstream distance. The piston effect of vehicles alone can provide 9-23% dilution of air pollutants in the tunnel, compounded to a 23-74% dilution effect according to the ventilation condition.

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

“…The problem is rather difficult to handle here due to the 3D geometry of the vehicles. Previous work by Chen et al (2002) modeled the piston effect of vehicle by having the fluid on the floor moving with the average traffic speed on the floor, thus resulting in an overestimate of fluid speed near the tunnel floor due to the neglect of non-slip conditions. However, tunnel studies by Chen, Lee, and Hsu (1998) indicated that the piston effect of vehicle causes the airflow to move at a speed approximately equal to the vehicle speed at a distance, z p ≒ 0.0625H, from the floor.…”

“…Chen et al (2002) simulated undersea traffic-tunnel flow and pollutant dispersion using the standard set of model constants. As to be seen later, because the dominant flow is unidirectional from tunnel inlet to tunnel outlet and traffic-tunnel flow is usually of low Reynolds number turbulent flow, the use of the standard k-e model is adequate in this study.…”

“…Although the design of lumped procedures is somewhat flexible and cost effective, non-uniform distribution of pollutants in the tunnel cannot be accounted for. However, advances in computer technology have enabled a detailed 3D, full-scale simulation of pollutant distribution in the tunnel (Chen, Chung, & Wang, 2002). Accurate knowledge of pollutant distribution in the tunnel is crucial for managing and controlling traffic and ventilation systems, as the demand of clean tunnel environment increases.…”

Three-Dimensional Modeling of Air Flow and Pollutant Dispersion in an Urban Street Canyon with Thermal Effects

“…Temperature measurements by Louka et al 29 in an urban street found that ⌬T is ϳ3 K at 9 a.m. and ϳ9 K at 6 p.m., and ⌬T ϭ 5 K was investigated numerically by Sini et al, 26 which are all commensurate with the range of 0 -5 K herein. The logarithmic function for a roughness wall was used in the velocity wall function, the same as that used in Chen et al 32 Also, the Jayatilleke function was used in the temperature wall function, the same as that in Kim and Baik. 27,36 The street roughness is specified as 3.8 cm, the same as in the previous work.…”

“…The procedures to estimate from the measured traffic flow rates have been described in related studies. 23,32 First, the rate of emission q ik (t) by traffic in the kth lane, of species i, is determined by:…”