Key outcomes

  • GHG emissions minimised
  • Plume dispersion target achieved
  • Regulatory requirements satisfied

Vehicle emissions form a large source of urban pollution. Inside tunnels, emissions result in reduced air quality, leading to requirements for tunnel ventilation. Emissions must be adequately dispersed to ensure safe environmental conditions both in the tunnels and near ventilation points. For full understanding of the three-dimensional flow structures inside tunnels computational fluid dynamics (CFD) is required. CFD can be used to predict the dispersion levels inside complex tunnel geometries, as well as resulting impacts on air quality and visibility.

Figure 1: Animation showing the Simulated exhaust plumes from trucks driving through a tunnel. The ventilation air extraction point is located to the left. The dispersion of emissions depends on many factors including the vehicle size, number of vehicles, speed of vehicles and the ventilation rate. Understanding the conditions within a tunnel enables the ventilation system to be optimised.

Synergetics engineers perform CFD simulations of ventilation inside tunnels as well as emissions near the tunnel portal and ventilation stacks. The results are used to optimise the emission strategy to minimise GHG emissions and achieve acceptable human health and environmental exposures.

Plume emitted from a road tunnel, showing how it travels along the road canyon before spilling over and being carried downwind

Figure 2: CFD simulation of the spread of the plume from tunnel portal emissions. The plume is coloured by wind speed, and is observed to spread slowly along the road canyon, before spilling over the barriers and being carried downwind.