Study of the Thermal Buoyancy on the Smoke Flow in Tunnel Fires under the Coupled Effects of the Longitudinal Air-flow and the Tunnel Slope

To understand the stratification of the smoke layer in a road tunnel, numerical simulations are employed to model tunnel fires with varying heat release rates. The different simulations cases are carried out with FDS (Fire dynamic simulations). These simulations are conducted to examine the influence of tunnel slope and longitudinal airflow on the smoke stratification along the downstream side of tunnel. The aim is to explore the relationship between longitudinal airflow and temperature ratio taking into account the tunnel slope. As a result, a quantitative analysis, based on Newman's theory, is conducted to assess the clarity of the smoke layer stratification, a Froude number (Fr = ۰.۶۳) is obtained. The slopes in tunnels can have a substantial impact on smoke flow during a fire, primarily driven by thermal buoyancy and the stack effect. With a slope less than ۱.۵°, the stratification improves. Similarly, clear stratification occurs when the longitudinal airflow is less than ۱ m/s. However, a balance between inertia force and buoyancy force is crucial for maintaining clear stratification. Increasing both the longitudinal airflow and the tunnel slope serves to disturb the stratification of the smoke layer.

Keywords:

Smoke stratification , Froude number , Longitudinal air-flow , Sloping tunnel