Developing a modelling approach for sound propagation through turbulent boundary layer and applying to train pantograph

Abstract

Sound propagation through turbulent boundary layer (TBL) is of great significance in transports where a TBL is attached to their external surfaces, for instance, air planes and high speed trains. Precise predictions of sound propagation through TBLs to their external surfaces can be extremely useful for their corresponding interior noise control. It is well known that a TBL is classified as an inhomogeneous flow medium and existing approaches are not capable to well predict its influence on sound propagation. Insight of sound propagation through TBLs is required but relevant research on this topic is limited in the literature. In this work, a modelling approach is developed to predict the influence of TBLs on sound propagation. In the proposed approach, the ray tracing method is employed to predict the evolution of sound waves when they are passing through a TBL, with which the equivalent phase speed of sound can be obtained and used to calculate the the Doppler factor so that the traditional methods can be extended to predict sound distribution in inhomogeneous flow media. The validation of this modelling approach is performed by using two cases. The first case is to predict the convective effect of sound propagation in a uniform mean flow and the predicted results are compared with analytical solutions. The second case is sound propagation through a TBL and the predictions obtained from this proposed approach are compared with numerical simulations obtained from the finite element (FE) method. In both cases, the convective effect obtained from this proposed approach is close to the analytical solution or the FE prediction. After that, the proposed approach is used to predict the sound propagation from a high speed train pantograph to the external surfaces of the train with considering the influence of the TBL. The corresponding results are verified by using FE simulations. This work shows that the proposed approach is effective and efficient, and also, it enhances the understanding of sound propagation in inhomogeneous flow media.