Numerical investigation on the effect of tunnel width and slope on ceiling gas temperature in inclined tunnels

Abstract

A series of simulations are conducted in full-scale inclined road tunnels to explore the effect of tunnel width and slope on ceiling gas temperature pattern in fire. Firstly, characteristic temperature pattern in inclined tunnel fires due to the presence of stack effect are indicated. The buoyancy induced airflow velocity at the inlet increases with tunnel slope and stays almost invariable with tunnel width, and the location of impinging point is blown downstream with the increasing tunnel slope and changes little with tunnel width correspondingly. However, the maximum ceiling gas temperature area stays almost unmovable with the change of tunnel width and slope because of the effect of the buoyancy induced airflow at the inlet on the upstream gas back-layering. Then a correlation of the maximum gas excess temperature with tunnel width and slope is proposed by dimensional analysis. Finally, taking the position and value of maximum ceiling gas temperature as references, downstream ceiling gas temperature data can be correlated well by an exponential expression. In addition, the correlation is compared with previous experimental results and simulated results in the tunnels with longer length and different fire source locations.