Investigating the influence of stack effect on plume inclination and maximum ceiling temperature position in inclined tunnel fires

Unlike horizontal tunnels, research on the maximum ceiling temperature position and its influencing factors in inclined tunnels is limited. This study employs numerical simulations to investigate the offset distance of the highest ceiling temperature position in inclined tunnel fires. The results indicate that the air inflow generated by the stack effect leads to an asymmetric air distribution around the fire source. The velocity of the induced air inflow shows a linear relationship with the magnitude of the stack effect. Different from the horizontal tunnel under longitudinal ventilation, the reason for the inclination of the plume is not only the wind, but also the tunnel slope and the stack effect. And the induced air inflow can well integrate the influence of these factors on the inclination angle of the plume. When the dimensionless induced airflow velocity is 0.1 or lower, the plume tilt angle corresponds to the residual angle of the tunnel slope, and the position of the highest temperature can be determined by multiplying the tunnel height by the tangent of the tunnel slope. Conversely, when the dimensionless induced airflow velocity exceeds 0.1, the plume tilts, and the location of the highest ceiling temperature shifts towards the tunnel entrance at a higher elevation. Prediction models for the induced airflow velocity, plume inclination angle, and offset distance are developed based on the examination of these influencing factors. These findings provide valuable insights for designing tunnel structures that can better withstand high temperatures.