2020 年 86 巻 888 号 p. 20-00025
Noise generated from Shinkansen trains mainly consists of wheel/rail noise, bridge noise and aerodynamic noise. Generally rolling noise and structure-borne noise from a viaduct increase in proportional to the second to third power of the train speed, whereas the aerodynamic noise increases in proportional to the sixth power of the train speed. Past studies showed that the aerodynamic noise becomes dominant at above 300km/h, and the main sources of the aerodynamic noise are the pantographs and bogies. In particular, aerodynamic bogie noise is important even if noise barriers are installed since the number of bogies are much larger than pantographs. This study focuses on the aerodynamic bogie noise for high-speed trains. A new measurement method is proposed to identify the source of the aerodynamic bogie noise precisely in wind tunnel test by using a porous plate. A part of the ground under a bogie is replaced by a porous plate which lets the sound wave propagates pass through while blocking off the air flow. This measurement method makes it possible to determine the sound source of the bogie in detail. It is found that traction motors and gear unit, which are located downstream in the bogie section, are dominant sound sources. Based on this knowledge, two mitigation measures for aerodynamic bogie noise are proposed. It is found that both of them reduce the aerodynamic bogie noise about 5dB in the frequency range of 250 to 315Hz.