## 1 Introduction  
In recent years, China's high-speed railway has achieved rapid development, the operational speed of the train has also been continuously improved. Train aerodynamic problems have become very significant [1; 2; 3; 4]. The aerodynamic drag force is approximately square with the train speed, and the aerodynamic noise is proportional to the 6-8 th power of the train speed [5; 6]. There are the objective laws that cannot be avoided by any form of ground transportation. To obtain the higher running speed near the ground, the fundamental way can only be to change the density of the medium. The cruising altitude of mainline aircraft reaches 10,000 m, which can remove the dense atmosphere. The ground train cannot fly to an altitude of 10,000 m. However, the closed tube can be used to reduce the density of the air, which is equivalent to creating a low-density medium environment around the ground train. Therefore, the ground train can be freed of the constraints of the aerodynamic drag force and aerodynamic noise, and in theory, can achieve higher running speed. The low vacuum tube high-speed maglev system combines a tube with a certain degree of vacuum and the high-speed maglev train, which can realize high-speed operation with low aerodynamic drag force and aerodynamic noise. In 1999, Oster and Fla received the patent for the invention of the vacuum tube transportation system. In 2013, [PERSON] proposed the plan for the Hyperloop. In China, in 2004, the academician's academic report \"Vacuum Tube High-speed Transportation\", jointly initiated by [PERSON] and [PERSON], was successfully held at the Southwest Jiaotong University, to discuss the scientific nature, reality, development prospect and great significance of the vacuum tube high-speed transportation system. In 2014, the world's first vacuum tube high-temperature superconducting maglev train experimental platform \"Super-Maglev\", which integrated traction, communication and pressure testing, was established in the State Key Laboratory of Traction Power of Southwest Jiaotong University [7; 8]. There has been an upsurge in research regarding vacuum tube high-speed maglev trains in the world. The research on the aerodynamics of the high-speed maglev train in the low vacuum tube is in its infancy, and the related research work is little. [PERSON] used the two-dimensional compressible model to study the relationship between the aerodynamic drag force of the high-speed train in the vacuum tube and train speed, blocking ratio, and tube pressure [9]. [PERSON] studied the influence of the blockage ratio, pod speed, pod length, tube pressure, and temperature on the aerodynamic drag force of the Hyperloop system, and found that the pressure drag force is significantly affected as the blockage ratio increased; strong shock waves occurred near the end of the pod as the pod speed increased [10]. [PERSON] and [PERSON] performed the aerodynamic shape design and optimization of the Hyperloop train body to ensure a certain aerodynamic lift force of the car body and reduce the aerodynamic drag force [11; 12]. [PERSON] and [PERSON] used two-dimensional dynamic grid technology to study the development of shock waves and the aerothermal effects inside the vacuum tube under unsteady conditions [13; 14; 15; 16]. [PERSON] established the parametric shape of the vacuum tube train, and took the aerodynamic drag force as the optimization objective. After the optimization, the aerodynamic drag force of the train was reduced by 5.52% [17]. [PERSON] studied the influence of the length of the streamlined head on the aerodynamic drag force of the train in the vacuum tube [18]. [PERSON] used the numerical simulation method to study the aerodynamic flow separation position of the vacuum duct aircraft, and optimized the aerodynamic shape of the aircraft [19]. The existing research work mainly focuses on the aerodynamic characteristics of the train in the low vacuum tube, and rarely involves the problem of the aerodynamic noise.