| High-speed maglev trains have the advantages of high operating speed,strong climbing ability,low energy consumption and less maintenance.It effectively fill the speed gap between air transport and traditional wheel-rail high-speed trains,and it has an indispensable supporting role and is the key development direction of the next generation of high-speed rail transit vehicles.During the "13th Five-Year Plan" period,China launched the National Key Research and Development Program Advanced Rail Transit Key Technology Research "High-speed Maglev Transportation System Key Technology Research",and began to develop 600km/h high-speed maglev train.The aerodynamic effect has a significant impact on the train’s energy saving and environmental protection,ride comfort,running stability and safety,and the train maglev system on the high-speed maglev train.The aerodynamic problem is one of the key problems in the design and development of 600km/h high-speed maglev trains.Therefore,it is necessary to systematically study the unsteady aerodynamic performance of the high-speed maglev train,and optimize the aerodynamic shape according to the key aerodynamic problems.In this paper,the unsteady aerodynamic performance of 600km/h high-speed maglev train when single train running on open lines with or without crosswind and two trains meeting were systematically studied by using the numerical simulation method.The key aerodynamic problems of high-speed maglev train running on open line were explored.Based on this,the main aerodynamic optimization objectives are slected,and the multi-objective aerodynamic shape optimization of the 600km/h high-speed maglev train head was carried out.The main research of the paper is as follows:1.The unsteady aerodynamic performance of the single high-speed maglev train running stably on the open line.For the five-carriage full-scale train model,using SST k-coturbulence model and improved delayed detached eddy simulation(IDDES),the unsteady flow field when the single train running on the open line,and the unsteady aerodynamic performance were investigated.The effects of steady flow and unsteady flow on the flow field and train aerodynamic force were studied,the law of influence of train speed and marshalling number on train aerodynamic performance was summarized.The results show that there are great differences in the train bottom structure and rail form between maglev trains and traditional wheel-rail high-speed trains,which lead to big differences in aerodynamic problems between the two trains,especially the lift forces.The pressure drag accounts for 21.5%of the total aerodynamic drag of the train,which is much smaller than that of the wheel-rail high-speed train.The aerodynamic lift of head car is much larger than that of other cars and its aerodynamic performance is the worst.Each aerodynamic forces fluctuate quasi-periodically around the time-average value,the maximum fluctuation range of the tail car’s lift force is 12.48%,and the maximum peak frequency of the lift forces’ power spectral density of each car is 9.3 Hz.The flow field structures of the transient simulation and the steady simulation are basically the same,but there is a significant difference in the wake zone.The differences in the aerodynamic force of the two simulation are small,and the maximum difference in the lift force of the tail car is 7.6%,which the steady simulation can be used to study the influence law of parameters on train aerodynamics.The aerodynamic forces of the head and tail car of the short marshalling can basically reflect the characteristics of the head and tail car aerodynamic forces of the long marshalling,the short marshalling train can be used to study the effects of train speed,wind speed,and wind angles on the aerodynamic performance of trains running on open lines.The aerodynamic drag forces and lift forces increases linearly with the square of the train speed.2.The transient aerodynamic performance of openline crossing.For the five-carriage fullscale train model,using three dimensional,unsteady,compressible N-S equations and SST kcoturbulence model,combined the overset mesh technology,the transient flow field,pressure wave and aerodynamic forces were investigated when two high-speed maglev trains crossing on the open line.The impact of the train speed on the pressure wave and aerodynamic forces were summarized.The results show that when two trains crossing on the open line,the pressure on the intersection side fluctuates violently and significantly.The fluctuation of aerodynamic drag is relatively small,and the fluctuation is mainly caused by the fluctuation of the pressure drag of the head and tail car.The friction drag of straight carriage is also has slight fluctuation.The lateral,lift,roll moment,yaw moment,and pitch moment have severe fluctuations,positive and negative transients in a very short period of time at the crossing,which seriously affect the stability and safety of train operation.There are no coupler constraints on the nose tips of the head and tail car,and the impact is even greater.Seriously,the aerodynamic performance of the head car is the worst.Both the pressure wave and the force’s peaks increase linearly with the square of the train speed.3.The aerodynamic performance of single train under crosswind.For the scaled threemarshalling train model,using SST k-ωturbulence model and the IDDES method,the unsteady flow field and aerodynamic forces of single train running on the open line under the crosswind were investigated.The effects of steady simulation and unsteady simulation on the flow field and train aerodynamic forces were studied,and the relationships between wind angle,wind speed,train speed and aerodynamic forces were summarized.The results show that the flow field and aerodynamic forces have significant unsteady behaviour under the crosswind.The flow field structures of the transient simulation and the steady simulation are basically the same.The difference between the aerodynamic forces of the two simulations is very small,the maximum difference is 2.55%.The steady simulation can be used to study the influence law of parameters such as train speed,wind speed and wind angle on the train aerodynamic forces.The crosswind increases the aerodynamic forces sharply,and the aerodynamic performance of the train deteriorates sharply,especially the head car and its performance is the worst.The running stability analysis of the head car can be used to evaluate the whole train.The wind angle,wind speed and train speed have a significant impact on the aerodynamic forces and flow field structure,and the relationship between wind speed,wind angle,train speed and the train aerodynamic forces can be expressed by a cubic polynomial function.4.Aerodynamic optimization of the head shape of the maglev train.Based on the parametric method of mesh free form deformation,the parametric model of the head was established.The mapping relationship between the nose length,nose height,nose width and the aerodynamic drag and aerodynamic lift was studied.Sample pointes were designed by using the optimal Latin Hypercube Sampling method and obtain the aerodynamic forces of the sample points through CFD.The Kriging approximate model was establish based on the sample points.The lift forces of the head and tail car and the drag force of the whole train were selected as the optimization objectives and based on the NSGA-Ⅱ algorithm to optimize the head shape.The results show that the aerodynamic drag of the whole train decreases with the increase of the nose length.The nose height and nose width have little impact on the drag force of the whole train.The lift force of the head car first increases and then decreases slightly with the increase in the nose length and width,and increases with the nose height.The change law of tail car’s lift force with design parameters is exactly opposite to that of the head car.Compared with the original head shape,the whole drag of the optimized head decreases by 4.22%,the head car’s lift force decreases by 35.67%,and the tail car’s lift force increases by 23.82%.The increased lift force of the tail car accounts for 26%of the reduced lift forces of the head car.It can be seen that the head car’s lift force decreases significantly,while the tail car’s lift force increases slightly.The optimized head effectively improves the head car’s lift force,and the lift force between the head car and tail car reaches a balance.The optimized head has the same trend of improving the aerodynamic performance under the crosswind as that without crosswind.The optimized shape has certain design robustness and universality in different running scene. |
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