Assessing competitive dynamic between buoyancy-driven smoke propagation and unsymmetrical centralized exhaust in tunnel complex

The buoyance-driven smoke propagation is the most harmful factor for both the rescuer and trapped people in tunnel fires. By centralized exhaust, it means to form a competition between buoyancy-driven flow and mechanical exhaust, and constricts the smoke propagation. This work explored the competitive dynamic of unsymmetrically centralized exhaust on constricting buoyancy-driven thermal smoke in tunnel complexes. The experiment was performed in a reduced-scaled apparatus of the tunnel complex, considering various exhaust flow rates, heat release rates, and the scheme of the exhaust vent, to find out the characteristics of buoyancy-driven smoke propagation and back-layering under unsymmetrically centralized exhaust. The findings indicate that the temperature decay of thermal smoke flow can be expressed exponentially, with the decay coefficient dependent on both fire heat release rates and exhaust flow rates. A dimensionless correlation integrating the effects of the exhausted heat and induced flow was developed to describe the stagnate point of thermal smoke. The result of this work not only enhances the understanding of the dynamic between buoyancy-driven smoke and centralized exhaust but also gives guidance to the design of ventilation systems in complex tunnel structures.