Abstract: The smoke stratification characteristics in the tunnel play an important role in analyzing the difficulty of evacuation and rescue and formulating effective emergency strategies. The smoke flow in inclined tunnels is affected by both buoyancy and stack effect, resulting in significant differences in the distribution and movement of smoke between inclined tunnels and horizontal tunnels. In inclined tunnels, the stability of smoke stratification is affected by many factors, and there are few related studies. In this paper, the numerical simulation method is used to study the smoke distribution characteristics and its influencing factors of inclined tunnel fires with openings at both ends with an inclination angle of 1%～15%. The research shows that the critical dimensionless temperature difference proposed by Newman to determine the stratification state of smoke is still applicable in inclined tunnel fires (the slope is within the range of 1%～15%). After the fire in the inclined tunnel, the smoke layer between the fire source and the low-end entrance can always maintain a stable smoke stratification. The smoke layer between the fire source and the high-end outlet increases with the chimney effect, and the area where the stable stratification is destroyed continues to expand and gradually expands to the entire downstream area. The fire source power and the height difference between the fire source and the high-end outlet can directly affect the stack effect in the tunnel and the smoke buoyancy, thus affecting the smoke stratification state. On this basis, a calculation model for predicting the smoke stratification characteristics of inclined tunnel fires is proposed, and the critical Froude number between zone 1 and zone 2 is determined to be 0.9. The research conclusions can provide useful reference for tunnel fire smoke exhaust and evacuation design.

Key words: inclined tunnel, smoke stratification, stack effect, Froude number