Abstract
The wind in subway systems is an airflow which is caused by the unsteady motion of trains in subway tunnels. Though the speed of airflow is sufficiently small compared with the sound speed, the compressibility of air should be taken into account in the case of closed space as like as subway systems. Blockage ratio σ=a/A is a parameter which denotes the effect of the compressibility, where “a” and “A” are cross sectional areas of the train and of the tunnel, respectively. For σ smaller than unity, a variable describing the compressibility is introduced in terms of fluctuations of mass density and of flow velocity. This is unitized to arrive at a set of self-consistent equations which governs the macroscopic behavior of the wind in subway systems. It is shown that the wind can be regarded as an incompressible except for the nearest neighborhood of the moving train in view of a nearly homogeneous flow.
Macroscopic justification is given through the comparison between model experiments and theoretical calculation.
