Experimental study on variable frequency control and air leakage control of multi-fan combination in subway tunnels

In centralized smoke exhaust emergency ventilation systems for metro tunnels, axial supply fans are often located far from the tunnel exit due to complex terrain constraints. This configuration creates a parallel-duct airflow path, causing a portion of the fresh airflow to bypass the traffic lane and escape directly through the exit, significantly reducing smoke exhaust efficiency. To address this leakage issue, this study takes the Wawuzhuang–Guizhou Road section of Qingdao Metro Line 1 as the engineering prototype and establishes a 1:10 scaled-down experimental platform based on similarity criteria, with a variable cross-section exit simulating a typical single-side leakage scenario. Four fan combination modes—comprising axial supply and axial exhaust fans—and 80 variable-frequency operating conditions were designed. Key parameters, including static pressure distribution, average airflow velocity in the traffic lane, and fan power consumption, were systematically measured. The effective smoke exhaust efficiency (ηe) was introduced as the core quantitative metric, and an equivalent length model was employed to parameterize leakage effects by converting abnormal operating states (e.g., tunnel exit leakage) into equivalent resistance increments in the ventilation system. Experimental results show that the configurations “dual-supply zero-exhaust” and “dual-supply dual-exhaust” exhibit higher leakage rates and lower ηe compared to “dual-supply single-exhaust”. Further comparison between “dual-supply left-exhaust” and “dual-supply right-exhaust” reveals similar leakage rates under identical frequency settings; however, when the exhaust fan frequency exceeds 18.5 Hz, the “dual-supply right-exhaust” configuration achieves significantly higher ηe than its left-exhaust counterpart, with ηe increasing by 3–5% per 1 Hz rise in exhaust frequency. This highlights the critical influence of exhaust fan placement on system performance. The findings indicate that, in centralized smoke exhaust metro tunnels, increasing the frequency of the axial exhaust fan positioned on the exit side can effectively mitigate leakage and enhance smoke exhaust efficiency, supporting the recommendation of the “dual-supply right-exhaust” fan configuration. This work provides crucial experimental evidence for optimizing fan combinations and frequency settings in long tunnels under extreme emergency scenarios—such as single-side exit failure—and offers practical insights for improving emergency smoke control and operational safety in tunnel systems.