Abstract
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.
Highlights
A moving train is the pressure source of the piston effect in a tunnel
The piston wind velocities in the actual tunnel can be obtained by using the model test results and velocity scale
A mathematical model of unsteady airflow was developed to discover the piston wind behavior induced by a braking train in a railway tunnel
Summary
A moving train is the pressure source of the piston effect in a tunnel. Piston wind has a significant effect on the smoke flow in a tunnel, especially in the rescue station after a train stops there [4]. Theoretical formulas are very effective to predict piston wind behavior. Tong et al [5] obtained a theoretical formula for the mean air velocity of the roof opening in urban vehicular tunnels based on energy conservation and mass conservation. They did not deduce a prediction formula for piston wind in a main tunnel. Zhang et al [7] developed mathematical equations to calculate the piston wind
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