| In the high-speed train aerodynamic scaled model experiments,the train models usually designed as 2-car model or 3-car model,while the full-scale high-speed trains were 8-car grouping or 16-car grouping.The difference of group-type whether affects the aerodynamic performance of high-speed trains or not,and the reduced length models can simulate the flow around full-scale trains accurately or not,are both concerned issues.With the high-speed trains popularizing in our country,different head-shape high-speed trains appeared.The different head-shape trains can cause different magnitude of tunnel pressure wave energy.The coupling aerodynamic effect between high-speed trains and tunnels caused our attention.Using moving model experiment method comparing and analyzing the geometric parameters of high-speed trains which include the group-type affects aerodynamic performance of high-speed train in this paper,the following contents studied:Using 1:8 scaled high-speed train models of China standard EMU CR400 AF in the moving model experiment,the slipstream at track-side of 3~8 car models were measured in the open air.The effect of group-type on slipstream was analyzed.The results show that the group-type length performed as length-width ratio of high-speed train models,different length-width ratio models perform different wake structures behind the tail of trains.The high-speed train model with smaller length-width ratio has narrower peak of slipstream and closer to the tail in the near-wake region.The 8-car model has maximum slipstream velocity,5-car model and 6-car model have lower velocity,and 3-car model,4-car model and 7-car model have similar low slipstream velocity;The maxima of slipstream are not confined to the near-wake region.As the group length grows,higher possibility of slipstream maxima exist is observed before trailing nose.Besides,The maxima of slipstream are not confined to the near-wake region.As the group length grows,higher possibility of slipstream maxima exist is observed before trailing nose.A CR400 AF 3-car model and a 3-car model which has similar head-shape,same body width and higher body height to CR400 AF measured slipstream at track-side in the moving model experiment,the effect of height of high-train’s body on slipstream was compared and analyzed.The results show that the different body height has negligible effect on slipstream velocity,but higher body of the model has farther peak velocity location to tailing nose than lower one.The stable state surface aerodynamic pressure of the 3-car~8-car high-speed train models was tested in the open air with moving model experiments;the stable state aerodynamic drag of 3-car model and 8-car model was measured in experiments.The effect of group-type length on surface aerodynamic pressure distribution and aerodynamic drag distribution among carriages.The results show that the surface aerodynamic pressure distribution along the max vertical centreplane profile and aerodynamic drag coefficient of head and tail hardly affected by the group-type length.The long grouping high-speed train’s aerodynamic drag bigger than short one’s just because the increased number of middle carriage cause the whole train aerodynamic drag increasing.The relationship between the situation of cross section variation and the initial compression wave was indicated by using 4 high-speed train models with different head-shape in the moving model experiment of passing through tunnel operating condition.The results show that the initial compression wave variation is the combined result of the average cross-sectional area and the cross-sectional area distribution of a high-speed train streamlined nose when the train’s max cross section and streamlined nose length are the same.The average cross-sectional area effects the magnitude of initial compression wave,and the cross-sectional area distribution effects the pressure gradient of initial compression wave,so that it effects the pressure dissipation of initial compression wave propagating in tunnel. |
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