Eulerian-Lagrangian model for traffic dynamics and its impact on operational ventilation of road tunnels

This contribution deals with a computational Eulerian-Lagrangian model that simulates movement of cars inside a road tunnel and its impact on operational ventilation. The model simulates moving cars as discrete objects that “fly” through the tunnel. The objects are treated with a Lagrangian momentum equation and their velocity is solved along their trajectories that are determined by the shape of the roadway. The flow of the ambient air is solved with a commercial CFD code StarCD. Due to drag force, the cars virtually change their velocity, but the latter is continuously re-set to its original value. The momentum equation for the continuous phase contains an additional source term that results from the net efflux of momentum of cars when they enter and leave a particular control volume of the solution domain. The model by Jicha et al. (Int. J. Environ. Monit. Asses. 65 (2000) 343) can simulate cars moving at different speeds and traffic rates in individual traffic lanes. As a result we obtain flow rate generated by moving vehicles as a function of traffic speed and traffic rates. Turbulence was modelled using standard k-ε model with three different formulas for extra sources of the kinetic energy of turbulence that account for additional turbulence generated by moving vehicles. The traffic-induced turbulence shows a non-negligible effect on the total flow rate inside the tunnel. The model was validated with experimental data from Chen et al. (Int. J. Wind Eng. Ind. Aerod. 73 (1998) 99), where the small-scale tunnel 1:20 was investigated. The experiments were carried out with a moving belt carrying small car-like objects. The tunnel length was 20 m, the height 36.5 cm and the tunnel had two parallel lanes. Several traffic densities and speeds were simulated, namely 10,000, 20,000 and 30,000 cars/h per lane with speeds of 20 km/h and 40 km/h.