Takami H., Kikuchi K., Iida M., Maekawa H., Kurita K.

When a high-speed train (called 'Shinkansen' in Japan) runs in an open section, low-frequency noise is radiated from the train toward the way-side area. The observed low-frequency noise, which is defined here as the noise of below 80Hz including the infrasound of 1-20Hz, consists of hydrodynamic pressure variations and acoustic pressure waves. The hydrodynamic pressure variations (also called a 'train passing pseudo-sound') are caused by the moving quasi-steady pressure field around the train nose, tail, and other uneven parts of the train. On the other hand, the acoustic pressure waves (also called a 'low-frequency pressure wave') are caused by the sources whose strength varies with time such as unsteady disturbed flow around the train and vibrating surfaces of a viaduct structure. While the former train passing pseudo-sound are well understood and can be quantitatively estimated, there remains much to be clarified as to the latter low-frequency pressure wave. This paper describes the characteristics of the way-side low-frequency noise based on the results of field measurement and model experiment. The measured results show that the major components of noise observed in the near field are the train passing pseudo-sound and those in the far field the low-frequency pressure wave. Judging from the measured characteristics of the low-frequency pressure waves (velocity dependency and distance attenuation), their major components are found out to be aerodynamic sounds emitted from a line source, especially in a high-speed region of over 350 km/h.