# A Review of Recent Research into the Causes and Control of Noise during High-Speed Train Movement
## 3 High-Speed Train Noise Research Methods
### Numerical Simulation and Theoretical Research  
To conduct train noise tests or wind tunnel tests relative to the various complex environments through which high-speed trains pass is costly, but the full range of flow field information can be determined quickly and easily through computational fluid dynamics (CFD). Computational fluid dynamics has various advantages, such as fewer restrictions and lower costs. Using the method of computational fluid dynamics, it is possible to use mathematical methods to discretize the flow field control equations in the grid of the computational region, solve the discrete numerical solutions, and obtain the aerodynamic noise of the train during travel according to the Navier-Stokes equations. As shown in Figure 4, the high-speed train model is huge and has a complex structure, so the mesh must contain many elements, often too onerous given current computational resources, to satisfy the need for a direct solution for the whole vehicle model. In CFD commercial software, the most common method is to ascertain the computational flow field characteristics by using [PERSON]'s acoustic approximation model and then use the acoustic analogy theory to simulate the noise propagation, thus improving the computational efficiency and saving computational resources.  
Many scholars have studied high-speed train noise using computational fluid dynamics. [PERSON] et al. [59] combined acoustic and fluid analyses to calculate the aerodynamic noise radiation from the surface vestibule side doors of high-speed trains. [PERSON] et al. [60] derived the far-field integral equation for aerodynamic noise and calculated the aerodynamic noise conditions at the train pantograph. [PERSON] et al. [61] developed a numerical model of the French TGV train based on the lattice Boltzmann method and obtained the noise distribution around a TGV high-speed train. [PERSON] et al. [57] and [PERSON] et al. [62] used large  
Figure 4: CFD meshing for high-speed trains. (**a**) Schematic of flow field computational domain [56]; (**b**) grid density variation in the computational domain [56]; (**c**) pantograph meshing [57]; (**d**) high-speed train complete grid [57]; (**e**) high-speed train head meshing [56]; (**f**) high-speed train head grid density variation [56]; (**g**) bogie meshing [58].  
eddy current simulation and boundary element method to simulate the pantographs of high-speed trains and found that the pantograph noise is concentrated in the low-frequency range, and the pantograph aerodynamic noise is gradually dispersed in the high-frequency range. [PERSON] et al. [63] conducted a simulation-based analysis of the pantograph and found that the slide plate, pantograph head, balance rod, insulators, bottom frame, and pull rod are the main sources of aerodynamic noise thereon. By comparing six models, [PERSON] et al. [64] found that the SST k-\(\omega\) method is the most suitable for numerical simulation of train aerodynamic behavior in crosswinds. To cope with the problem of insufficient computational resources during the numerical computation of high-speed trains, [PERSON] et al. [65] proposed a model for pantograph noise prediction based on the Reynolds number provided by a single component.  
As shown in Figure 5, CFD software can give you the calculation results of running train vortex shedding. The rapid development of computers in the future will further promote the development of numerical simulation and theoretical research into high-speed trains to provide more abundant solutions to the noise problems associated with high-speed trains.