Numerical Study On Air And Smoke Flow Characteristics In Subway Space

Based on Beijing typical subway station and tunnel, three-dimensional CFD (computational fluid dynamics) method was used to study air environment under both normal and fire emergency conditions. Some simulation results are compared with in-situ measurements and small-scale experiments. Main research works include:The influences of the piston wind caused by train's movement, PSD (platform screen door) and air-conditioning system on air environment were investigated using transient numerical simulations. Some in-situ measurements were conducted to validate the simulations. The results show that over 5 m/s air velocity and 4℃temperature enhancement is aroused by piston effect in some platform locations. Air flow rate through tunnel ventilating shafts increases greatly after full closed PSD is installed on the platform. 2.5 m high partial closed PSD has not distinct influence on air flow rate through the exits and tunnel ventilating shafts.Numerical simulations and small-scale experiments were conducted to study the effect of the longitudinal ventilation on tunnel fire smoke movement characteristics, the critical ventilation velocity, the maximum smoke layer temperature and the relationship between the critical ventilation velocity and the back-layering temperature above fire source for different fire source conditions (heat fire source and combustion fire source) and heat release rates. The simulation results were compared with the previous study and the small-scale experiments. It shows that the choice of the fire source model has significant influence on simulation results. Simplified heat source without consideration of the combustion mechanisms (heat fire source) would over predicate the critical velocity. The down stream smoke layer temperature under the critical ventilation state predicted by simulations with different fire source models are higher than that measured in small-scale tests.The influence of the heterogeneous air velocity field caused by piston wind on smoke movement characteristics in subway tunnel was studied using three-dimensional CFD method. The results show that as the train fires and stops in the tunnel, the inertial air velocity field has significant influence on smoke movement characteristics at the first few minutes of fire disaster, which should be considered in setting reliable fire evacuation plan.