Beschreibung:
Critical velocity is very important to smoke control in longitudinally ventilated subway tunnel fires. Theoretical analysis and numerical simulations are conducted in this paper to investigate the impacts of metro train obstruction on critical velocity in sloping subway tunnel fires by using fire dynamics simulator (FDS). Moreover, a global model of critical velocity is presented for sloping subway tunnel including influencing factors of obstruction ratio, obstruction-fire source distance, and tunnel slope. The results show that critical velocity decreases with increasing of metro train obstruction ratio linearly. The change rate of critical velocity is smaller than that of metro train obstruction ratio. Aerodynamic shadow zone behind subway train obstruction has important impacts on critical velocity. Critical velocity increases or decreases with increasing of obstruction-fire source distance for fire source in aerodynamic shadow zone behind metro train, which is determined by the local recirculation airflow. There is an optimum ventilation velocity which can have the shortest back-layering length when fire source locates in the aerodynamic shadow zone very near metro train obstruction. Critical velocity increases with increasing of tunnel slope in sloping uphill subway tunnel. The global models can predict the critical velocity in a sloping subway tunnel with train blockage accurately