Behavior of Piston Wind Induced by Braking Train in a Tunnel

It is critical to discover the behavior of piston wind induced by a braking train in a tunnel, but there is little research on the theoretical derivation for piston wind behavior. Predicting piston wind behavior as an unsteady airflow by a theoretical formula is hard work due to the complexity of train running states and airflow fields. Herein, we develop a mathematical model to investigate the behavior of piston wind as an unsteady airflow, considering the variation of wind direction in the annular area. In general, the theoretical model is validated by experiments. However, experimental studies about piston wind are scarce. In this study, we simulated the emergent braking process of a train to validate the mathematical model by establishing a 1/50 scaled experimental configuration. The piston wind data tested in the experiment have good agreement with the results calculated by theoretical formulas. In addition, sensitivity analysis of the effect parameters of piston wind (i.e., tunnel length, train length, train speed and blockage ratio) was conducted. The theoretical formulas derived in this paper are applicable to similar train running conditions in railway tunnels or subway tunnels.