Numerical and experimental research on flow and aerodynamic noise characteristics of coach

Abstract

The researches on flow and aerodynamic noise characteristics of coaches are urgently needed to improve with the rapid development of new energy coaches. In this paper, tests in model wind tunnel and numerical calculations were carried out to study the phenomenon of flow and aero-noise on 1:25 scale model coach. Based on large eddy simulation (LES) and detached eddy simulation (DES), reliable numerical calculation method of flow and aero-noise on coach was established and verified. It is found that the maximum difference on turbulent pressure between test and LES is less than 10 dB(A) while that of DES is about 20 dB(A). Due to the results got from 1:25 scale model, the W_LES_HOA model is used to obtain the flow field and sound field information outside the coach. To find out the different propagation characteristics of turbulent pressure pulsation and acoustic pressure, proper orthogonal decomposition (POD) and band-pass filter analysis are used for further analysis. For rearview mirror, the energy of first mode is 6.1%, and only the first nine modes have an energy for more than 3.0%. By the reconstruction of first four modes, it can be seen that the complicated transverse vortex shedding couples with A pillar vortex and reaches the body surface. However, the coupling of turbulent pressure can only be seen clearly under low frequency around 250 Hz while the coupling of acoustic pressure can be seen under 750 Hz. Meanwhile, with the analysis of low frequency round 250 Hz and 500 Hz, the change of flow field generated by airflow impingement on the windward surface and A pillar makes the front of the coach becomes the main sources of aerodynamic sound sources.