Numerical study on fire smoke movement and control in curved road tunnels

This study presents numerical results for critical ventilation velocity and smoke movement for fires in different transverse positions in curved tunnels. The highest critical velocity is observed for a fire positioned next to the convex wall in a curved tunnel where the critical velocity is 16% higher than a fire located centrally in the same curved tunnel which has a curvature radius of 600 m. Critical velocity is observed to vary slightly with curvature, being 7% larger in a 400 m radius tunnel compared to a fire in a straight tunnel. This could be attributed to generally lower speed flows near the convex wall in curved tunnels, and this effect diminishes with larger curve radii. As a consequence, higher smoke temperatures at the ceiling are found for fires near the convex wall in curved tunnels, and tunnel ventilation speed has to be increased to prevent the smoke back-layering in curved tunnels. Additionally, three regimes of back-layering length are concluded for the transverse fire locations in this paper. The first is for a fire next to the tunnel wall, where the back-layering length increases slowly as the air speed tends to be lower than the critical velocity, followed by a rapid rise. Secondly, as a fire moving away from the wall, the back-layering length increases at a gentle gradient. The back-layering length is shortest in this circumstance. A fire in the middle lane and a fire in the lane near convex wall are considered as regime 3. The back-layering length evolution is steepest. Here the back-layering length increases significantly as the tunnel curve radius decreases for the same air speed.