Field study on the through-draught characteristics and its influencing factors in subway carriages

Abstract

The through-draught effect inside a subway significantly impacts the flow field profile, thus causing a potential threat to pollutant dispersion and human health. This study conducted multiple field measurements to systematically analyze the through-draught characteristics during actual train operation. The results show that the total variation of airflow velocity has a high consistency with train operation parameters, which reaches its peak value at the end of the acceleration period (EAP). And the airflow direction reverses as the running speed falls to nearly 0.45 times the maximum of that. For the whole subway train, the air velocity grows continuously in the first four carriages and then drops from the fifth carriage, with a maximum speed of 2.37 ± 0.12 m/s. Moreover, the airflow velocity distribution in a carriage exhibits an approximate “W-shape”, and the profile of the maximum airflow velocity is equivalent to a “parabolic surface”, with a velocity difference of less than 0.45 m/s. Finally, the through-draught effect is comprehensively affected by train acceleration and station spacing which further impact the air inertia forces and internal pressure difference, respectively; the wind speed peak positively correlates with train acceleration and subjects to an inverse exponential function with the station spacing. The research outcome can provide a valid basis for airflow control and air quality improvement in subway carriages operating in the underground tunnel.