# Aeroacoustic Optimization Design of the Middle and Upper Part of Pantograph
## 1 Introduction  
Existing research shows that when the train speed is greater than 300 km/h, the proportion of aerodynamic noise source energy to total noise source energy is about 50% [1; 2; 3]. The pantograph is one of the main aerodynamic noise sources. Pantographs are composed of bars of different scales and inclination angles, which induce complex flow field phenomena such as layer/turbulence boundary layer separation, vortex streets, flow transitions, and large separation turbulence, and become significant noise sources [4; 5]. In terms of pantograph region aerodynamic noise characteristics and generation mechanism, the acoustic wind tunnel test results of [PERSON] and others [5] show that the pantograph has obvious wind-blown sound characteristics, and its far-field radiated noise has Strohal number similarity. [PERSON] et al. [6] calculated the closed pantograph aerodynamic noise for 300 km/h using SAS and acoustic boundary elements and pointed out that vortex shedding is the main formation mechanism of pantograph aerodynamic noise. [PERSON] et al. [7] and [PERSON] et al. [8] both analyzed the aerodynamic noise contribution rate of pantograph components and obtained some accurate conclusions, for example, the high-frequency noise mainly originated from the bow head. [PERSON] et al. [9] studied the sound generation mechanism of the external convex cavity deflector around the pantograph and found that the transverse vortex dislodged from the cavity guide edge hit the cavity with the edge and generated a strong fluctuating pressure inside the cavity. In terms of pantograph aerodynamic noise optimization measures, the main focus is on optimizing the rod aerodynamic shape, adding deflector structures, etc. [PERSON]. [10] et al. explored in detail the acoustic characteristics of the guide edge shape, its cross-sectionalshape, and the inclination angle of the pantograph deflector, and designed a new low-noise deflector with a decreasing 2 dB. [PERSON] et al. [11] and [PERSON] et al. [12; 13] all pointed out that suitable bow-head struts can destroy its vortex street, thus effectively suppressing its radiated noise. [PERSON] et al. [14] showed that the noise radiated from an open pantograph is 3.4 dBA lower than that of a closed one. [PERSON] et al. [15] used the LES, FW-H equation, and genetic algorithm-based Kriging model to optimize the cross-sectional shape of the bow head, and the optimal cross-sectional shape of the bow head with optimal aerodynamic/acoustic characteristics was obtained. The optimized effect of 26% drag reduction and 2 dB noise reduction was achieved. [PERSON] et al. [16] numerically investigated the flow/acoustic field characteristics of a cylindrical rod with different angles of attack and incoming flow velocities and found that the higher the angle of attack, the lower the peak sound pressure level and frequency of aerodynamic noise. [PERSON] et al. [7] pointed out that optimizing the shape of the deflector can effectively suppress the cavity radiation noise. [PERSON] et al. [17] simplified the pantograph and sinking platform into a cylinder and a concave cavity, respectively, discussed the influence of the position of the cylinder installation and the rounding angle of the guide edge on the aerodynamic noise and obtained the following conclusions: the backflow length of the cavity and the vortex are significantly reduced during the growth of the circular angle from 0 to a certain angle, and the total radiated aerodynamic noise, total resistance and total lateral force are also significantly reduced; increasing the distance between the guide edge and the cylinder can effectively suppress the mutual interference behavior between the shear flow and the cylinder, thus reducing the peak sound pressure level.