Multifaceted analysis of air age-pollutant-thermal comfort in urban tunnels under forced ventilation
Huijun Wu, Bo Long, Zhuwei Xie, Yimin Xiao
Abstract
To mitigate the risk of poor working environment caused by inefficient forced ventilation in urban tunnels, the influence of vortex formation on the air quality, thermal comfort, and pollutant discharge capacity using numerical simulation and field measurements was investigated in this study. Then, an evaluation framework based on Criteria Importance Through Intercriteria Correlation (CRITIC) and Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) was constructed to comprehensively assess key indicators, including air age, particle residence time, particle number, and apparent temperature. The results revealed a trade-off between pollutant discharge capacity and thermal comfort on the one hand, and air quality on the other, under forced ventilation conditions. Small air duct diameter had a positive effect on reducing both particle number and average apparent temperature in working zones within 3 m ahead of the excavation face, but it adversely affected the average air age and average particle residence time. Furthermore, when a dimensionless air duct diameter (i.e., ratio of the air duct diameter to the hydraulic radius of the tunnel cross-section) of 0.426 was adopted, the forced ventilation achieved an optimal overall performance in terms of air quality, pollutant discharge capacity, and thermal comfort, with a comprehensive performance score 8.6 % superior to that obtained with a dimensionless diameter of 0.682. This study provides valuable insights for enhancing forced ventilation design and improving environmental health in urban tunnel construction.