The optimization study of the operational ventilation system for long tunnels on secondary highways

Long tunnels and extremely long tunnels on highways are becoming increasingly common. As tunnel lengths continue to increase, pollutants in the air can easily accumulate inside the tunnels, leading to air quality that fails to meet driving requirements, which poses health risks to drivers and passengers. This paper uses the Donggang Mountain secondary highway long tunnel as the engineering background and establishes a 1:1 full-scale model using the numerical simulation software Fluent. It studies the extreme traffic congestion conditions in long highway tunnels, exploring the distribution patterns of pollutant gas concentrations within the tunnel and the role of the longitudinal ventilation system under different operating conditions in reducing tunnel pollutant gas concentrations and improving air quality. Furthermore, the study investigates the ventilation efficiency of a combined ventilation method using ventilation shafts and jet fans. Compared to the full jet longitudinal ventilation method, the carbonic oxide (CO) concentration growth rate after the ventilation shafts decreased by 50%.