Study on near-field aerodynamic noise in the upper region of a full-size, full- formation subway train on open line based on the acoustic fluctuation equation

With the rapid development of urbanisation and regional economic zones, higher operational speeds (up to 200 km/h) are required for subway trains. This paper constructs a near-field noise model for a full-scale subway train operating at 200 km/h on an open track, based on Large Eddy Simulation (LES) and the Acoustic Wave Equation. The study primarily investigates the flow-field characteristics and noise evolution mechanisms in the pantograph and windscreen areas. The results indicate that with the pantograph in the lowered position, its folded structure and the air-conditioning system form a semi-enclosed cavity, creating a downstream ‘dead water zone’ characterised by low-speed, high-vorticity flow, where aerodynamic excitation is more intense compared to the raised pantograph condition. When the pantograph is raised, its wake features multi-scale vortex shedding and interacts with downstream components. In the windscreen area, upstream local asymmetric geometric structures, such as the layout of motor bogie air ducts and insulators, further amplify downstream pulsating pressures and acoustic radiation. Specifically, pulsating pressures at Windscreen 1 are concentrated on one side, while vortex shedding from the wake of the raised pantograph invades the cavity of Windscreen 3 and couples with its natural modes in the low-frequency and harmonic ranges, causing concentrated and biased pressure distributions. Consequently, the noise levels at Windscreen 3 are significantly elevated compared to those at Windscreen 1 and Windscreen 2. This study provides new theoretical references and practical insights for analyzing aerodynamic noise coupling mechanisms in the middle and upper regions of next-generation subway trains with complex configurations and for optimising noise control strategies.