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The application of positive pressure ventilation technology in a multi-layer subway station is quite complicated due to the large space and complex structure. In order to investigate the positive pressure ventilation effectiveness in an oversized underground space, a series of numerical simulations using the large eddy simulation method were conducted, based on a three-layer subway station case. The range of critical average exhaust speed and average supply speed in restraining smoke spread were obtained, and the smoke control effects under these conditions were analysed. The airflow velocity distribution at a long staircase was obtained. The findings show that as airflow moves downward, airflow velocities in corresponding locations decrease due to energy loss. Some weak locations were identified where smoke is difficult to restrain. Moreover, smoke control optimization designs are presented in this paper by changing smoke exhaust and air supply parameters. The simulation results indicate that the mechanical exhaust volume could influence the smoke control effect more significantly than air supply volume. The work presented in this paper can provide a significant reference to optimal design for the smoke control and personnel evacuation in multi-layer subway stations.

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