Train-induced airflow effect on coupled heat and mass transfer in a permafrost tunnel

Abstract

When a high-speed train passes through a tunnel, it disturbs the original airflow state in the tunnel, which is an aerodynamic and thermodynamic process. This process involves complex heat and mass transfer in the coupled fluid-solid system. To date, more attention has focused on train-induced aerodynamic forces, waves and acoustics in tunnels, and energy transfer has received limited attention. Needless to say, few studies have the train-induced airflow effect on coupled heat and mass transfer in permafrost tunnels. To solve this problem, we built a numerical model for the Fenghuoshan tunnel in permafrost regions based on three conservation principles and then simulated the aerodynamic and thermodynamic responses to a high-speed train. When the train enters the tunnel, a large mass of air is pressed from outside to the inside of the tunnel, and the air in front of the train is pushed and speeded up. A high-pressure zone appears in front of the train, while a low-pressure zone forms behind the train tail. Under the action of a pressure gradient, the air rapidly flows toward the low-pressure zone. In addition, the moving train disturbs the original airflow state in the tunnel. The train-induced airflow raises the air temperature in the permafrost, and the maximum rising temperature of the air can reach 1.6°C. The heat energy in the air gradually transfers into the surrounding permafrost, causing the permafrost to thaw and reducing the tunnel's safety. Therefore, the train-induced airflow effect on the heat and mass transfers in permafrost deserves our attention and further study.