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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.

The reduction of the aeroacoustic bogie noise that is generated by the Shinkansen high-speed trains travelling faster than 300 km/h is an important environmental issue. Currently, the amount of aeroacoustic bogie noise can be quantitatively estimated at the measuring points based on a spatial distribution of the sound pressure level (SPL) that is obtained by a two-dimensional microphone array in a wind tunnel test. However, it is necessary to appropriately consider noise generation and sound field with respect to various acoustic properties such as ground reflection and insertion loss of a bogie side cover. In this study, the transfer function between the integrated spatial distribution of SPL and the results that are obtained by an omnidirectional microphone are calculated by a numerical method. The aforementioned transfer function is calculated based on the bogie conditions that the side cover would be set and that the ground reflection effect would also be included. The transfer function is observed to change significantly in the lateral direction in low-frequency regions, especially in the 125 and 160 Hz bands. These spatial trends are also confirmed using an acoustic test that is based on the reciprocal theorem, and it is observed that these trends are caused by the interference between the reflection waves from the ground, the cavity upper wall, and the side covers. The SPL of the aeroacoustic bogie noise of Shinkansen trains can be estimated using this transfer function and can be compared with the results that are obtained from the field tests.

A method has been developed for predicting the aerodynamic noise from the bogie of a high-speed train using a two-dimensional microphone array in a low-noise wind tunnel. First, the mean velocity distribution of flow was simulated precisely in the low-noise wind tunnel. Next, aerodynamic noise generated by the bogie, hereinafter referred to as aerodynamic bogie noise, was estimated from the noise source distribution measured with the two-dimensional microphone array. Finally, based on the experimental results, the predicted noise generated from the lower part of the car (i.e. the total of the aerodynamic noise estimated through the proposed method and the rolling and machinery noise estimated in a previous study) was compared with the measurement data obtained near the track in the field test. It was found that the predicted sound pressure level showed good agreement with those measured in the field test. This suggests that the proposed method is appropriate to estimate the aerodynamic bogie noise quantitatively. It was also shown that the contribution of the aerodynamic bogie noise to the total noise generated from the lower part of the car is greater than that of rolling and machinery noise, especially below 500 Hz.