Study of the Diffusion Law of Harmful Gases in Tunnel Construction on Plateaus and Optimization of Ventilation Parameters

[Image: see text] To explore the diffusion law of harmful gases near the excavation face in tunnel construction on plateaus, select the optimal ventilation parameters, and improve the ventilation efficiency, Ansys Fluent was used to set the environmental parameters according to the highland, where the tunnel is located, and simulate and curve fit the diffusion phenomenon of CO and NO(2) based on the fluid control equations and species transport model. The effects of air velocity, ventilation time, and duct position on the diffusion law of harmful gases were analyzed, from which the optimal ventilation conditions were selected, and the ventilation effects under the optimal conditions were compared with those under the original conditions. The study shows that after the fresh airflow passes through the outlet, part of it flows out along the tunnel wall toward the cave entrance, and the other part interacts with the return air to form a vortex; when the air supply speed is 10 m/s and the distance from the duct outlet to the excavation face is 25 m, the maximum concentration of harmful gases decreases by 92–99% after 20 min of ventilation compared with that before optimization and the smoke exhaust efficiency increases by 2.5% per minute.