###### Abstract  
Flat roofs and platform sinking are two common installation configurations for high-speed pantographs. The cavity formed by the platform sinking is a potential source of aerodynamic drag and noise. In this paper, the shape of the rectangular cavity is optimized, and the aerodynamic performance of the high-speed pantograph with or without platform sinking is compared and discussed based on the optimized cavity results. The flow field and sound propagation are predicted by the improved delayed detached eddy simulation (IDDES) method and the FW-H equation. The results show that the rectangular cavity produces the largest aerodynamic drag and radiation noise. The upstream, downstream, and bottom surfaces of the cavity can be optimized by rounded and sloped edges to reduce aerodynamic drag and noise. The unstable shear flow and recirculation zone formed by flow separation and reattachment can be reduced by modifying the upstream and downstream surfaces of the cavity. In addition, the vortex in front of the downstream surface of the cavity can be reduced or even eliminated by modifying the bottom surface. When the upstream and downstream surfaces of the cavity are rounded and the bottom surface is sloped (\(R/H=0.8\)), the aerodynamic performance of the cavity is better. Compared with the pantograph installed on the flat roof, the aerodynamic drag and noise of the pantograph with platform sinking are significantly reduced due to the shielding of the lower structure by the cavity, and the total drag and noise are reduced by 5.22% and 1.45 dBA, respectively. high-speed pantograph; platform sinking; aerodynamic drag and noise; reduction; numerical simulation +
Footnote †: _Applied Sciences_
generated by the pantograph on the train surface through numerical simulation. The noise generated by the pantograph installed on the flat roof will significantly affect the train body surface near the pantograph. The farther away from the pantograph, the smaller the sound pressure level. In addition, the author also points out that flow can facilitate sound propagation upstream. [PERSON] et al. [9] carried out bionic optimization of the pantograph strips. By reducing the flow separation and recirculation zone on the surface of the strips, the surface fluctuation pressure is reduced, resulting in drag and noise reduction of the pantograph. Pantograph installation platform sinking can significantly reduce the aerodynamic drag of the widely used pantograph. However, studies have shown that the noise level of the cavity formed by the platform sinking is similar to that of the pantograph [10]. [PERSON] [11] evaluated the effect of pantograph recess on the flow field and noise through wind tunnel tests. It is pointed out that the pantograph recess is similar to the cavity, and the downstream area of the cavity is the main source of noise. The interaction between the cavity flow and the pantograph structure will increase the upstream turbulence intensity and decrease the downstream turbulence intensity. [PERSON] et al. [12] numerically simulated the aerodynamic noise of a pantograph with and without a cavity. The airflow separates from the leading edge of the cavity and interacts with the pantograph to generate a large fluctuating pressure on the structural surface. The flow field velocity distribution around the pantograph with a cavity is smaller and the radiation noise is lower. [PERSON] et al. [13] studied the flow-induced vibration of an open cavity by wind tunnel test. The turbulent shear layer provides a noise source for the self-excited oscillation of the cavity. The excitation source is broadband noise, and some frequency components are amplified into tonal noise under certain conditions. Based on previous studies, the noise reduction of pantograph recess has not been considered in depth. Therefore, this paper optimizes the shape of the installation platform to achieve aerodynamic drag and noise reduction.