Trains in tunnels

Abstract This chapter describes the nature of the flow in railway tunnels and forms the basis for the consideration of a number of practical issues in tunnel aerodynamics in Chapter 12 . The nature of the pressure transients caused by trains passing through tunnels is discussed in detail, and in particular the large changes in pressure as the train enters the tunnel are described. The concept of wave diagrams is presented, and the way it can be used to describe wave interactions is illustrated. The various factors that are associated with tunnel pressure changes are set out and discussed. In addition to the pressure changes, velocity changes in tunnels as trains pass through are also presented. The effects of airshafts on both tunnel pressures and velocities are then considered. Finally, the issue of micropressure waves (or sonic booms) from the exits of tunnels is discussed – both in terms of their generation through the steepening of entry pressure transients and their radiation outside the tunnel.