Theory of the Piston Effect : Two Fluids Piston Model

Abstract

The Piston effect means the uniform airflows are caused by the motion of trains in a tunnel. Interactions between a moving train and the air are discussed theoretically to clarify behaviors of the uniform airflows. The two fluids model are used as the basis of the theory. A variable to describe the interaction is presented in terms of fluctuations of density and velocity of airflows in the region between the train and the tunnel wall. This is utilized to derive a set of self-consistent equations which govern the behavior of uniform airflows. Justifications of the theory are made by the comparison between field tests and numerical calculations based on the equations.