Study On Aerodynamic Heating Characteristics Of High-speed Maglev Train In Low-vacuum Tube

With the development of economy and technology of the society,the speed of traveling is demanded further.People begin on imagining a kind of convenient and fast super-high speed ground transportation system.When the running speed of the traditional wheel/rail train exceeds 400 km/h in a dense atmosphere,the aerodynamic drag of the train will account for more than 80%of the total drag.At the same time,the wheel/rail train is restricted by the problems of wheel/rail adhesion,aerodynamic noise,hunting instability and pantograph-catenary relation etc.As a result,the traditional wheel/rail train is difficult to break through to a higher speed.Based on this,the super-high speed transportation system combining low-vacuum tube and high-speed maglev is born at the right moment,making it possible to achieve the ground super-high speed transportation at 1000 km/h and higher speed.Some new aerodynamic problems arise consequential when the super-high speed train running in airtight tube.With the increase of the train speed,aerodynamic heating problems emerge gradually.Heat quantity generated by aerodynamic heating in the tube when the train runs does not radiate out through the surrounding airflow as easily as it does in the open air.Instead,due to the limitation of the airtight tube,the heat quantity accumulate in the tube much more easily,raising the temperature inside the tube.As a result,the strength of the train body and the tube may be affected,which will further endanger the system’s safety.Therefore,combining with the suspension characteristics of HTS(high-temperature superconducting)maglev,the aerodynamic heating characteristics of the tube train are studied by numerical calculation method in this paper.The motion of high-speed maglev train in the tube is simulated based on three-dimensional,steady,compressible Reynolds-averaged Navier-Stokes equation,SSTκ-ωtwo-equation turbulence model and the principle of relative motion at the airflow and train in wind tunnel model.The rationality of the numerical method is verified by the experiment data of ONERA-M6 airfoil.Taking the HTS maglev train model with cross-section areas of 9.637 m~2 and the tube with cross-section areas of 34.418 m~2(the blockage ratio of 0.28)as the research object,this paper mainly studies the influence of air pressure,train running speed and initial ambient temperature on aerothermal environment,aerodynamic force and flow field structure in tube.The main works and conclusions are as follows:(1)When the wind tunnel model is adopted to calculate the flow field of the tube train,the boundary condition(fixed wall and moving wall)of the tube may have a great influence on the numerical results.Therefore,after comparing the numerical calculation results of the fixed wall and the moving wall,this paper chose the moving wall which is more reasonable.(2)Considering that when the train runs at low pressure environment,the change of air pressure in the tube will have a certain influence on the flow field around the train.Hence,the influence of different pressure(0.1～0.5 atm)on the flow field is briefly studied.The results show that the change of air pressure has little influence on temperature of the train surface,temperature field and flow field structure in the tube,but has great influence on aerodynamic drag of the train and pressure of the train surface.And aerodynamic drag of the train increases approximately linear with the increase of air pressure.(3)When the train runs in the tube at a transonic speed of 1000 km/h,there will be a local supersonic area accompanied by shock waves in the flow field.In this paper,the characteristics of the flow field in the tube under the train running at transonic are analyzed.Showing that there is a local supersonic,low temperature and low pressure areas in the wake,and the appearance of shock waves make the flow field structure in the wake area more complicated.(4)The change of train running speed has great influence on the aerothermal environment in the tube.The paper discusses the influence of different train speed(500～1250 km/h)on the aerothermal environment in the tube.Indicating that temperature distribution on the head and tail of the train presents a large gradient,and the maximum temperature on the train surface generally appears at the stagnation point of the head,while the temperature gradient on the surface of middle train is small.The average temperature rise on surface of the middle train increases with the train speed,which is similar to the quadratic curve.When the train speed is 500 km/h,the average temperature rise on surface of the middle train is about 8 K,and that of 1250 km/h is about 76 K.In addition,the structure of the temperature field near the train also varies greatly with the increase of train speed.When the shock wave appears in the flow field,the higher the train speed,the longer the low temperature region in the wake.(5)For the continuous running tube train system,the temperature in the tube may gradually increase due to the heat dissipation of equipment carried by the train and aerodynamic heating,in the practical application of tube train in the future.The initial ambient temperature in the tube may be different for trains running at different times.Therefore,the influence of the initial ambient temperature on the flow field in the tube is studied.It is found that increase of the initial ambient temperature can effectively reduce the aerodynamic drag of the train.When the initial ambient temperature increases from 243 K to 393 K,the aerodynamic drag of the train decreases by about 40%.At the same time,increase of the initial ambient temperature can help to shorten the supersonic,low pressure and low temperature region in the wake of the train.In the future engineering applications,considering that the temperature stress caused by excessive temperature difference may affect the normal operation of the equipment in the tube,the temperature inside the tube can be maintained at a reasonable value.In addition,appropriately increasing the ambient temperature can also reduce the aerodynamic drag of the train.