Effect of asymmetric slope of mainline on smoke movement characteristic in bifurcated tunnel fire under natural ventilation

Tunnel fires can cause significant casualties and property damage. Most of the existing researches are focused on single-tube and horizontal bifurcated tunnel fires that the smoke movement characteristics in a bifurcated tunnel with asymmetric slopes are barely studied. This work numerically investigated the effect of mainline asymmetric slopes on smoke movement characteristics in a bifurcated tunnel. Five mainline slopes (0%, 1%, 3%, 5%, 7%) and four heat release rates (5 MW, 10 MW, 15 MW, 20 MW) were carried out. The maximum temperature rising and longitudinal decay beneath the tunnel ceiling were analyzed. Results show that the maximum temperature rise in the mainline tunnel was inversely proportional to the mainline slope. The effect of mainline tunnel slope on temperature longitudinal decay is limited, but the heat release rate has a substantial impact on the ceiling temperature in sloped tunnel region. The empirical equations for maximum temperature and temperature longitudinal decay was developed by considering the mainline slope.