Parameter optimisation and efficiency evaluation of oxygen supply system in high altitude tunnel based on orthogonal test-Fluent coupling

This study addresses the oxygen supply challenges in high-altitude tunnel construction under low-pressure and low-oxygen conditions. A three-dimensional numerical model of tunnel ventilation and oxygen supply was developed using Fluent software and validated against field measurements. Through orthogonal experimental design, the effects of three key parameters—oxygen pipe layout position, distance between the air duct and the tunnel face, and oxygen pipe extension length—were systematically investigated. The results reveal a ‘rapid rise–slow stabilization’ temporal evolution pattern of oxygen volume fraction distribution. Using the oxygen volume fraction compliance rate at the working face as the evaluation index, range analysis was employed as the primary method to determine factor significance and establish the sensitivity ranking of parameters. Furthermore, Pearson correlation analysis was applied to quantitatively validate the reliability of the range analysis conclusions by measuring the linear correlation strength between each factor level and the comprehensive evaluation index. The results indicate that the distance from the air duct to the tunnel face is the most significant influencing factor, followed by layout position and oxygen pipe extension length. The optimal parameter combination was identified as vault layout, 20 m duct-to-face distance, and 2 m oxygen pipe extension, achieving an oxygen volume fraction of 25.83% and a 100% compliance rate at the working face. The findings provide theoretical and practical guidance for the design of oxygen supply systems in high-altitude tunnels and suggest directions for future research, such as multi-field coupling simulation and intelligent oxygen supply strategies.