采用PyroSim数值模拟方法系统研究不同排烟功率对相向射流条件下顶部集中排烟系统吸穿现象的作用机理。深入分析了排烟效率提升对隧道内烟气层厚度、温度分布以及气流速度的变化规律。研究确定了对于不同火源热释放率下吸穿现象发生的临界排烟效率，给出相向射流条件下集中排烟发生吸穿现象的临界Froude数和预防吸穿现象发生的临界排烟速率系数。研究结果表明：随排烟功率增加，远离火源的排烟口R3率先发生吸穿现象，继而排烟口R2也发生吸穿，而R1未受影响，火源热释放率的增大导致发生吸穿现象的临界排烟功率相应增大。适度提升排烟功率可以提升排烟效果，但排烟功率超过特定临界值将发生吸穿现象，使排烟效率降低。在20、30、50 MW火源热释放率下，临界排烟功率分别为80、100、150 m³/s，最佳排烟功率分别为50、70、110 m³/s。同时，确定了发生吸穿的临界Froude值为35，临界排烟速率系数为0.8。研究结果为优化排烟系统设计、提升效率和节能提供理论依据。

Utilizing the PyroSim numerical simulation method, a comprehensive study was conducted to investigate the mechanism of the smoke pull-through phenomenon in a top-central exhaust system under conditions of counter-flowing jets, with a focus on the effects of various exhaust powers. Changes in smoke layer thickness, temperature distribution, and airflow velocity within tunnels were investigated under conditions of enhanced exhaust efficiency. Critical exhaust efficiency thresholds associated with smoke pull-through phenomena were identified across varying heat release rates of fire sources. Furthermore, the critical Froude number for smoke pull-through in centralized exhaust systems was established under counter-flowing jet conditions, along with the critical exhaust rate coefficient required to prevent such occurrences. The findings revealed that as the exhaust power increased, the exhaust port R3, located farthest from the fire source, was the first to experience smoke pull-through, followed by R2, while R1 remained unaffected. An increase in the heat release rate of the fire source led to a corresponding rise in the critical exhaust power threshold for smoke pull-through. A moderate increase in exhaust power could improve exhaust performance; however, exceeding a specific critical value would trigger smoke pull-through, thereby reducing exhaust efficiency. At heat release rates of 20 MW, 30 MW, and 50 MW, the critical exhaust powers were identified as 80 m³/s, 100 m³/s, and 150 m³/s, respectively, with optimal exhaust powers of 50 m³/s, 70 m³/s, and 110 m³/s. Furthermore, the critical Froude number for smoke pull-through was determined to be 35, and the critical exhaust rate coefficient was 0.8. These findings provide a theoretical basis for optimizing the design of exhaust systems, enhancing efficiency, and promoting energy conservation.