Alleviation of Pressure Rise from a High-Speed Train Entering a Tunnel

When traveling through a tunnel, a high-speed train generates pressure waves that propagate back and forth to the portals and affect passenger comfort. Part of the initial compression wave is also radiated at the tunnel's far end, as a micropressure wave, causing environmental nuisance. The strength of this micropressure wave is proportional to the slope of the initial compression wave produced upon train entry, which depends on the geometry of the train and the tunnel entrance and on the blockage ratio. This paper presents a review of the current state of understanding of tunnel entrance aerodynamics for high-speed trains and an experimental assessment of the performance of countermeasures to reduce the slope of the initial pressure rise. A parametric investigation makes use of a scaled-model experimental facility for analyzing the effect of the train velocity and different configurations (conic-shaped train noses, flared portals, vented portals, etc.) on the initial compression wave. It is shown that replacing an abrupt entrance with a progressive one has a beneficial effect on the gradient of the compression wave. A less-costly civil engineering construction consists of distributing ventilation along the tunnel entrance. Among the several distributions tested, the experimentally optimized distribution of the tunnel portal ventilation reduces the slope of the initial pressure rise by a factor of 6.