A novel type of unpowered air curtain at a tunnel portal to reduce the intrusion of cold air

Abstract

In modern cities in cold regions, where the average ambient temperature is always below 0 °C during winter, an increasing number of subway lines are being constructed due to the rapid development of urban traffic. Cold air intrusion is caused by train operation, and natural ventilation will pose a risk of freezing equipment at the tunnel entrance and affect the regular operation of the subway line. However, there is still a lack of established efficient and energy-saving methods to control the cold air invasion of tunnels. In this paper, a new curved tunnel structure installed at the entrance of a tunnel can form an unpowered air curtain, and the installation method and optimal structure of the curved tunnel are determined by numerical simulation. In this research, by optimizing the four dimensionless geometric parameters of the curved tunnel structure, a primary optimized structure with a flow reduction rate of 18.79% is obtained. In addition, the flow reduction rate of the curved tunnel can be increased to 37.29% by adding a deflector at the curved tunnel entrance. The optimized results are verified by a scale model experiment, ensuring the accuracy of the proposed structure. This paper provides guidance for the study of controlling cold air invasion at tunnel portals.