Analysis of flow and aerodynamic noise behaviour of a simplified high-speed train bogie inside the bogie cavity

Aerodynamic noise becomes significant for high-speed trains but its prediction in an industrial context is difficult. The flow and aerodynamic noise behaviour of a simplified high-speed train bogie at scale 1:10 are studied here through numerical simulations. The bogie is situated in the bogie cavity and cases without and with a fairing are considered, allowing the shielding effect of the bogie fairing on sound generation and radiation to be investigated. A two-stage hybrid method combining computational fluid dynamics and acoustic analogy is applied. The near-field unsteady flow is obtained by solving the unsteady three-dimensional Navier-Stokes equations numerically using delayed detached-eddy simulation and the data are utilized to predict far-field noise signals based on the Ffowcs Williams-Hawkings acoustic analogy. Results show that when the bogie is located inside the bogie cavity, the shear layer developed from the cavity leading edge interacts strongly with the flow separated from the bogie upstream components and the cavity wall. Therefore, a highly turbulent flow is generated within the bogie cavity due to flow impingement and recirculation within the cavity. It is found that, for noise calculated from the bogie surface sources of both cases, the directivity exhibits a lateral dipole pattern with dominant radiation in the axial direction. Compared with the no fairing case, the noise level is about 1 dB higher in the bogie symmetry plane along the axle mid-span for the fairing case where a stronger flow interaction is produced around the bogie central region. Moreover, the noise radiated to the trackside is predicted based on a permeable integration surface close to the bogie and parallel to the carbody side wall. The results show that the bogie fairing is effective in reducing the noise levels in most of the frequency range due to its shielding effect and a noise reduction around 3 dB is achieved for the current model case by mounting a fairing in the bogie area.