Streamline Structure Optimization And Aerodynamic Characteristics Analysis Of High-speed Trains In Confined Spaces

In the Vacuum Tube Transportation System(VTT),trains travel at high speeds in narrow,low-pressure confined spaces,and issues that are not prominent at low speeds(aerodynamic drag,lift,aerodynamic noise,etc.)cannot be ignored.These problems greatly reduce the comfort and safety of passengers,and become the main factors restricting the realization of VTT.To realize the idea of VTT as soon as possible,it is necessary to study and improve its aerodynamic performance.The design of high-speed train heads involves complex strong fluid-structure coupling problems,and the fundamental method to solve these problems is to carry out multi-objective optimization of the train head.In this paper,a three-dimensional model of the head shape of a high-speed train in a limited space is established,and the length of the nose tip L and the head height H of the train are used as the optimal design variables,and the aerodynamic drag and lift are the optimized goals.Using grid automatic deformation software Sculptor,CFD calculation software Fluent and multi-disciplinary optimization design software Isight for joint simulation,the automatic deformation of the grid and the automatic calculation of the flow field in the system are realized,and the design variables are automatically optimized based on genetic algorithm and automatic optimization of head shape.After the optimization is completed,the key design variables that affect the optimization target drag and lift are obtained,and the correlation between them is analyzed.A series of Pareto optimal head shapes are obtained through multi-objective optimization.Research shows that the length of the train head has a greater impact on drag,with a contribution rate of 38%;the height of the train head can have a greater impact on the lift received by the train,with a contribution rate of 33.6%.The nonlinear relationship between the optimization goal and these two design variables is studied.The design variable "H" is positively related to the optimization goal "lift" with a correlation of 0.739.The design variable "L" and the optimization goal "drag" are positive correlation,the correlation is 0.911.Finally,by comparing the original streamlined head shape,the optimized aerodynamic resistance of the high-speed train can be reduced by up to 2.89%,and the lift can be reduced by up to 1.96%.In addition,in order to explore the distribution law of aerodynamic noise of high-speed train in vacuum tube,a calculation model of aerodynamic noise of high-speed train in vacuum tube under low-pressure environment is established.Using a combination of theoretical research and numerical simulation,based on the Lighthill acoustic analysis method,numerical calculations are made of the aerodynamic noise distribution law,body surface acoustic power,spectral characteristics,and sound pressure of high-speed trains in vacuum tube under low pressure.By establishing a physical and mathematical model of three-dimensional flow around a high-speed train in a confined space,the external steady-state flow field of the high-speed train under different blocking ratios and different operating speeds in a low-pressure environment is numerically simulated.Simulation results show that the aerodynamic noise of high-speed trains in confined spaces is caused by pulsating pressure on the surface of high-speed trains due to external flow.The air flow is easy to separate,the relative velocity is large,and the pressure gradient is large where the turbulent motion is severe,the isobar is relatively dense and the pulsating pressure changes are also more intense,which is the main sound source area of the train body.After spectrum analysis,the pulsating pressure on the surface of the train body has a broadband characteristic;Based on the k-? double equation turbulence model,the surface noise sources of high-speed train bodies in confined spaces at different blocking ratios and different operating speeds were calculated.The simulation results show that under different working conditions,although the distribution of noise sources on the surface of train body is similar,the intensity of the sound source is very different.The sound power level of the train body will increase significantly with the increase of the train running speed and the blocking ratio.Based on the SST k-? turbulence model,the far fieldaerodynamic noise of high-speed train in the confined space is simulated.Through sound pressure level and frequency spectrum analysis,the far-field aerodynamic characteristics of the vacuum tube train were obtained.The simulation results show that the spectrum characteristics of the sound pressure at the measurement point do not change significantly with the increase of speed.