Numerical Simulation of Tunnel Ventilation Considering the Air Leakage Mechanism of a Ventilation Duct

Ventilation problems are critical in tunnel engineering, and the loss of air volume in ventilation ducts is generally estimated using empirical methods. The air volume calculation makes it difficult to meet the accuracy requirements, resulting in resource waste or insufficient air supply. In this study, the forced ventilation system of the tunnel under construction was investigated based on the computational fluid dynamics method. The mechanism of air leakage on airflow distribution and pollutant transport in the tunnel is determined. Air leakage reduces the distribution peak of pollutants and effectively accelerates the emission of harmful gases. However, this effect decreases with distance from the air duct inlet. Through the calculation results of nearly one hundred models, it is found that the air leakage of the duct can be fitted by logarithmic function and verified by empirical equation. The matching degree between the fitting function of the model and the empirical equation depends on the length of the tunnel. On this basis, the calculation formula of effective air volume near the working face is derived. This study can be applied to the ventilation engineering of the tunnel under construction and provide a theoretical basis for the calculation of the effective air supply.