29. Wind tunnel tests for detailed detection of sources of aerodynamic noise from bogies

The main sources of aerodynamic noise from a railway vehicles running at high speed are the head car, pantographs and bogies. Work is ongoing using RTRI’s large-scale low-noise wind tunnel facility to find ways to reduce aerodynamic noise generated by bogies, however, it has not been possible so far to clearly detect the exact location of aerodynamic noise sources in a bogie through lateral acoustic investigations because the bogie is fully covered.

Therefore, the ground plate beneath the bogie was replaced with a sound transmission board, which allows sound waves to pass through but blocks air flow, and a microphone array was installed beneath the board. The proximity of the microphone array to the bogie made it possible to accurately distinguish the sources of aerodynamic bogie noise (Fig. 1).

The results from tests using this method identified the main sources of aerodynamic bogie noise to be the traction motor and the gear unit among others (Fig. 2). An acoustic test using a speaker confirmed that the influence of the sound transmission board on measuring the location of sound source was sufficiently small.

By using the developed measurement method, it will be possible to locate various sources of aerodynamic noise, and contribute to the reduction of aerodynamic bogie noise.