Ceiling jet velocity during the whole process of fire development in a tunnel

When a tunnel fire occurs, the response speed of the ceiling-mounted smoke or thermal detector is of great significance for controlling the fire. The information on the ceiling jet flow is important for detector installation and design. In this paper, a series of numerical simulations and experiments are conducted to investigate the jet flow velocity in tunnel fire during different stages. The ceiling jet flows velocities in the development stage and the stable stage are presented. When the growth rate of the fire source is very fast, the ceiling jet flow velocity in these two stages can be supposed as the same. A simple correlation of the velocity is developed and the predicted results are in good agreement with numerical values and experimental values. The gas flow driven by the thermal expansion at the beginning of the tunnel fire is also discussed. A prediction model of the gas expansion velocity is proposed.