The effect of tunnel cross section size on the fire plume characteristics of train fires

High-speed railways are increasing the demand for longer and larger cross section tunnels in order to shorten transit times and enhance transport capacity. In order to investigate the effect of different tunnel cross section sizes on the fire plume characteristics of stationary train fires, a novel scale-resolved hybrid turbulence model based on k–ω shear stress transport was used to simulate stationary train fire scenes in four tunnel cross section sizes (48, 59, 70, and 80 m2). The reliability of the numerical simulation strategy employed in this study was verified by conducting small-scale tunnel train fire model experiments. The results show that when a fire occurs at the bottom of the head car, the longitudinal temperature and smoke concentration distributions in the tunnel roof are asymmetrically distributed, and that the peak fire plume temperature and peak smoke concentration decrease with increasing tunnel cross section. The size of the tunnel cross section has a significant effect on the downstream smoke dispersion range, with the 80 m2 tunnel increasing the downstream smoke dispersion range by 52 m compared to the 48 m2 tunnel. It is worth noting that in this study, a refined grid strategy was adopted to clarify the evolution of the fire plume, which strikes the tunnel roof laterally and mixes with the air along the tunnel walls in a coiled fashion; in the longitudinal direction, the fire plume spreads in waves toward the tunnel ends.