Influence of tunnel slope on movement characteristics of thermal smoke in a moving subway train fire

In this study, the three-dimensional unsteady Navier-Stokes equation and fully buoyant corrected Renormalization-group (RNG) k-epsilon turbulence model were employed to investigate the influence of tunnel slopes on the temperature distribution characteristics of a subway train moving with a fire source. The sliding grid technology was used to simulate the relative movement between the subway train and tunnel, and its reliability was verified by moving train fire experiments. It was found that the slipstream primarily determines the movement of the smoke when the subway train carries fire in transit. After the train stops, the residual slipstream drives the smoke downstream of the fire source. As the slipstream is attenuated, the smoke eventually flows backward. The influence of the tunnel slope on the temperature distribution law is mainly exhibited after the train stops. With the increase of the tunnel slope, the time elapses before the smoke counterflow increases, while the upstream temperature decreases. It was found that when the tunnel slope increased from 3% to 1%, the counterflow of smoke was delayed by 86 s.