Geometrical influence of structures in close proximity to a railway wheel on its sound radiation

The most important noise source from railways is rolling noise. It is produced by vibration of the track and wheel, which is induced by their combined surface roughness at the wheel/rail contact. The component of noise radiated by the wheel is generally often the greatest above 2 kHz. The current models used to predict the sound radiation from the wheel consider this to be in free space; in practice, however, the rail beneath the wheel, the ground in close proximity and the bogie frame around it have geometrical effects on the wheel radiation. This paper investigates their influence in terms of the sound power and the directivity at 7.5 m from the track center. The sound radiation of a single wheel in free space is analysed first by using the combination of vibration finite element method and acoustic boundary element method in 3D. The geometry of the rail and ground beneath the wheel are then introduced and their effects on the wheel radiation are predicted. The bogie frame is also introduced to find its influence on the sound radiation from the wheel.