High-Speed Vehicles in Low-Pressure Tunnels—Influence of Choked Flows

The aerodynamics of high-speed vehicles in evacuated tunnels is studied with particular reference to the consequences of choked flow conditions at the tails of the vehicles. It is shown that this has a dominant influence on overall conditions (pressure, temperature, velocity). Together with the need for the evacuated tunnel system to be closed, the high speeds cause the aerodynamic behaviour to differ greatly from that in conventional railway tunnels. A key purpose of the paper is to assess the relative importance of a large range of parameters and, for clarity, this is completed by focussing on a single vehicle in a single tunnel that is closed at both ends. Consideration is then given to interactions between more than one vehicle and to a twin-tube tunnel configuration in which interactions occur between vehicles moving in opposite directions. The paper closes with a brief mention of system-dependent matters that need to be considered in addition to the generic parameters investigated herein.