Multiple steady states of fire smoke transport in a multi-branch tunnel: Theoretical and numerical studies

The multiplicity of smoke flow states may pose a great threat to both human evacuation and emergency rescue in tunnels. A case study is conducted to investigate the multiple steady states of fire smoke transport in a triple-branch tunnel. Both theoretical analysis and numerical simulation are employed in this study. For the case examined in this study, at least three flow regimes are identified under the effects of similar boundary conditions. The results indicate that even for a “well-designed” smoke exhaust system, multiple flow regimes could exist and some flow modes could threaten the human evacuation. The operating point of the mechanical fan system shifts due to the transition between multiple flow regimes. The preliminary results indicate that the inclination angle of the inclined tunnel branches could play an important role in the multiplicity of smoke flow states in such a tunnel system.