Research on the mechanism of metro wheel high-order polygons affecting sound pressure level

This paper analyses the effects of several typical polygon amplitudes and orders on wheel sound radiation in metro lines using the finite-element method (FEM) and the boundary element method (BEM). A vehicle–rail coupled rolling contact model incorporating wheel polygons is established, and the wheel–rail forces under different polygon amplitudes and orders are obtained. The corresponding wheel sound radiation results are also obtained. The results demonstrate that the model accurately reflects the impact of polygons on wheel–rail forces. Polygons increase inter-wheel–rail forces, and higher polygon orders result in greater wheel–rail forces for both standard and resilient wheels. However, the wheel–rail forces do not exhibit a linear relationship with polygon amplitude. Furthermore, the noise reduction mechanism of resilient wheels is thoroughly explained in terms of damping, energy dissipation, vibration isolation, decoupling, and acoustic impedance characteristics. By changing the polygon amplitude, order, and track line, it was found that, within the 400–5000 Hz frequency range, the higher the polygon orders, the higher the sound pressure level (SPL) for two types of wheels. Polygon amplitudes differ, with the resilient wheels radiating SPL 2–13 dB(A) lower than the standard wheels in the 2500–5000 Hz frequency range. No significant linear relationships were found between the polygon amplitude and the SPL of the two types of wheels in most frequency bands. Additionally, the SPL of the resilient wheels is 3–10 dB(A) lower than that of the standard wheels in the 2500–5000 Hz band under curve conditions. Moreover, under curve conditions the rubber layer of the resilient wheels reduces the SPL at a high speed and frequency.