The distribution of pantograph aerodynamic noise on train external surfaces and the influence of flow

Abstract

Aerodynamic noise from the pantograph is significant when a train is running at high speeds and can be important for noise inside the train as well as at the wayside. In this work, the propagation of noise from a pantograph to the train external surfaces is studied, including the influence of the air flow. The noise emitted by the pantograph is modelled using a semi-empirical component-based approach which allows for the main factors of influence. To calculate the distribution of sound on the train external surfaces, the waveguide boundary element (2.5D BE) method is first employed, in which the pantograph is modelled by several equivalent dipole sources. Laboratory experiments are used to verify the 2.5D BE model for predicting the noise around the train due to the pantograph. The pantograph noise is found to be quite localised on the roof directly below the pantograph, where the sound pressure level on the train surface is high, but with increasing distance from the pantograph, it decreases rapidly. Moreover, the difference between the sound pressure level on the train roof and on the sides is about 20 dB in the plane of the pantograph. The influence of flow on the sound propagation is then modelled by introducing the profile of the velocity in the boundary layer into a 2D finite element model using the linearised potential flow model in COMSOL Multiphysics. The air flow causes some amplification in the sound pressure levels in the upstream direction and attenuation in the downstream direction. At high frequency the wind gradient in the boundary layer will change the direction of the sound, leading to the formation of a quiet shadow area in the upstream direction. However, despite these effects, the flow has only a small effect on the region with the highest noise levels beneath the pantograph.