Influence of train Mach number on the compression wave generated in a tunnel-entrance hood

Abstract

A continuum theory is proposed to study the influence of distributed windows on the compression wave generated by a train entering a tunnel-entrance hood at high Mach numbers. Longer, acoustically noncompact hoods must be used to control the wave-front characteristics at train Mach numbers M between about 0⋅25 and 0⋅4. A train entering a fully optimized hood of length lh produces a compression wave wherein the pressure increases linearly over a wave front of thickness ∼lh/M. When M exceeds about 0⋅2, the interactions of the train nose with windows at opposite ends of the hood become progressively more independent. For a hood whose windows are optimized for low Mach numbers, we show that high-Mach-number operation produces a rapid increase in pressure at the head of the compression-wave front, generated just as the nose enters the hood portal. The pressure rise becomes substantially smoother and close to linear when the nose is within the body of the hood, within the relatively homogeneous environment provided by the distributed windows.