Theoretical modeling of the flows fields formed by Train-induced piston wind and ventilation jets in subway platforms for isothermal conditions

Abstract

In a subway platform without screen doors, ventilation jets are obviously influenced by the dynamic platform piston wind, coming from the tunnel as a result of a train entering and leaving the platform. The coupled dynamic airflows of platform piston winds and air jets are the most typical air organization on platform, significantly affecting the thermal comfort of passengers and the energy consumption of the air-conditioning system. In this study a theoretical model for the velocity characteristics of the coupled airflows is developed, based on the existing cross-flow theory for isothermal conditions. The expressions of the coupling airflows’ trajectories, length, and horizontal angles are derived, as well as their axial and horizontal velocities. The dynamic variation characteristics of typical velocity parameters are studied during train pulling in process by using the theoretical model. The trajectories switch to the right direction at first, keep biggest and stable later and decrease to the initial free jet finally. Totally the whole dynamic duration of the coupled airflows is about 110 s. Besides, the profiles of the above parameters are analyzed at some typical moments. At 35 s and 70 s, the horizontal velocities have the maximum peak value with the vertical distance to the vent 151 cm. These studies provide important theoretical guidance and references for optimizing the thermal environment design and operation of subway control system.