Numerical investigation of longitudinal location and heat release rate of fire source on neutral plane height and induced flow in longitudinal sloping tunnel fires under natural ventilation

This study investigates numerically the impact of the longitudinal location as well as the heat release rate (HRR) of the fire source on the neutral plane and induced flow within a longitudinal sloping tunnel under natural ventilation. Research shows that neutral plane height in longitudinal sloping tunnels is mainly influenced by the longitudinal location of the fire source and the longitudinal slope and is relatively insensitive to the HRR. The nearer the fire source location is to the low entrance and the greater the slope, the higher the neutral plane position at the high entrance of the tunnel will be. In addition, the induced flow between the fire source and the low entrance of the tunnel was compared for all conditions. Results indicated that the induced flow velocity was positively correlated with the longitudinal slope of the tunnel and the HRR, and negatively correlated with the distance between the fire source and the low entrance of the tunnel. Eventually, a non-dimensional model was established to estimate the velocity of the induced flow between the low entrance of the tunnel and the fire source. These conclusions have implications for the field of tunnel fire safety engineering.