Tunnel aerodynamics issues

Abstract This chapter, building on the description of tunnel pressures and flows in Chapter 6 , discusses a range of practical issues associated with aerodynamic effects in railway tunnels. Firstly, pressure transients in tunnels are considered, and the range of methods used for calculating pressure transients in tunnels is set out, together with their input requirements. Aural pressure comfort is then considered, and the pressure transient limits specified by standards are described, together with an overview of the experiments from which these standards were derived. A probability-based approach to assessing aural comfort is also provided. Methods of reducing these pressure transients are then presented – through modification of tunnel geometry and train operating conditions, through the provision of airshafts or through the sealing of trains. Secondly, the emission of micropressure waves from tunnels is considered. Methods to reduce the inlet pressure gradients (and thus to reduce the magnitudes of these waves) are described – tunnel entrance hoods, elongated train noses, provision of cross shafts and the use of both passive and active aerodynamic damping devices. Finally, the chapter describes a range of other tunnel aerodynamic issues – train drag in tunnels, structural loading in tunnels and on trains and the very specific problems associated with long tunnels.