Study on optimization design of air supply uniformity for a double-layer air duct in metro vehicle

To address comfort issues caused by uneven airflow distribution in subway vehicle passenger cabins, a full-scale numerical model of the cabin and air supply duct was developed using computational fluid dynamics. This model was employed to analyze flow field characteristics, resistance, and airflow distribution within the duct. Based on these findings, an optimization strategy incorporating flow guide plates was proposed. Furthermore, the impact of this optimization on flow and temperature fields within the passenger cabin under full-load conditions was investigated and evaluated using the thermal comfort index. The results showed that in the original air supply duct, airflow accumulates in regions farther from the air supply vents, leading to lower airflow near the vents and excessive airflow in distal areas. Additionally, resistance and airflow exhibit an inverse relationship. The optimization process involved iterative adjustments of the flow guide plate design, including perforation ratio and relative positioning, based on flow field characteristics. The implementation of flow guide plates significantly improved air supply uniformity, reducing the nonuniformity coefficient by 0.23 for perforated plates and 0.08 for non-perforated plates. The optimized duct design enhanced passenger cabin comfort by reducing the maximum airflow velocity and average temperature by 0.11 m/s and 1.47 °C, respectively. Both horizontal and vertical temperature differences, as well as the thermal comfort index, met the relevant standards. This study provides a scientific basis and valuable reference for future research on optimizing air supply uniformity in railway passenger cars, contributing to enhanced comfort and improved airflow distribution in existing subway vehicles.