Reproducing the flight behavior of falling debris from railway tunnel vault using a high-speed train ejection experiment and moving-overset-mesh simulation

Falling debris in high-speed railway tunnels is a prevalent and serious safety concern. Debris falling from tunnel vaults may impact the train surfaces, pantographs and window glasses, resulting in economic losses and even injuries to individuals. The complex train winds inside a railway tunnel are a nonnegligible factor influence the flight trajectory and impact position of falling debris. Therefore, understanding the flight behaviors of falling debris considering the train wind effects is crucial for engineering managers to make informed decisions that improve the operational safety of high-speed trains in tunnels. In this study, we develop a device that controls the automatic drop of a tunnel debris in a high-speed train ejection experiment. By employing the experiment and moving-overset-mesh method, the flight behavior of falling debris from the vault of a railway tunnel under the influence of train winds, including the translation behavior, rotation behavior, aerodynamic coefficient, and corresponding flow mechanism, are investigated. The reliability of the high-speed train ejection experiment is confirmed through repetitive tests. The moving-overset-mesh simulation is verified by a grid independence test and comparisons with the experimental results. The research findings unveil a distinctive two-stage flight behavior of falling debris influenced by the wind generated from the passing train. Specifically, the first stage of debris flight is primarily governed by the wind profile near the train body, while the second stage is characterized by the tail airflow. Moreover, there exists a difference in the flight behavior between square and circular plate debris, which can be attributed to the variation in distribution and scale of vortex structures that form and adhere to the falling debris.