Acoustic Properties of Aerodynamic Bogie Noise Generated from Shinkansen Train

Aerodynamic noise generated from a bogie section of High -Speed train (aerodynamic bogie noise) is one of the major noise sources and becomes dominant in a low frequency region when the train runs above 300 km/h. In the previous study, aerodynamic bogie noise by using 2-D microphone array in a low noise wind tunnel has been estimated. It was 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 noises, especially below 500 Hz. The train bogie is installed in the cavity under the train body. The sound generated from noise sources in the cavity is affected by side covers and a ground. Therefore, it is important to know the acoustic characteristics, e.g. acoustic path from the noise sources to measuring point close to the train, the change in SPL due to the side covers of the bogie cavity and the ground. In this study, in order to investigate these acoustic characteristics, acoustic test are carried out by using a 1/7 scale train model in an an-echoic room. On the reciprocity theorem, microphones in the cavity and a speaker at the measuring point are set, respectively. The effects of these boundary conditions, e.g. the side covers and the ground, on the SPL at the evaluation point are measured by installing microphones inside the bogie cavity and the speaker at the evaluation point, respectively. The sound reflections on the side covers and the ground are identified by using the impulse response. Based on these results obtained in the test, the influence of the boundary condition on these acoustic characteristics is discussed.