Research On Aerodynamic Characteristics And Operation Safety Of High-speed Trains Under Cross Winds

High-speed train is of complicated shape and high slenderness ratio, it causes three dimensional viscous flow that is complex and strongly nonlinear. When high-speed train runs in crosswind, the flow field and aerodynamic performance will change, as well as wheel-rail dynamic performance, thus influenting the safety of high-speed train on operation. There has been a substantial amount of research carried out to investigate the effects of crosswind on high-speed train and the aerodynamic safety in different parts of the world at present, while in the fields of complicated scene modeling, crosswind aerodynamic analysis, crosswind unsteady properties, and the influence of crosswind aerodynamics on safety of running train, remain to further investigation.Based on method of combining theoretic analysis, model test, flow numerical simulation and multi-body dynamics simulation, issues of crosswind aerodynamics of train and the relevant track dynamics were numerical simulated and analyzed by taking CRH high-speed train as the research object, and issues of train safety control in crosswind were studied. The main contents include the following parts:1. Aerodynamic performance of single car in open air and cross wind was studied. The results show that the different value of aerodynamic force between simulation with uniform wind and that with lower atmospheric boundary layer wind, is20%-60%, and the value is relative to road conditions such as flatland, embankment and bridge, as well as the location of train. So there is obvious deviation from the actual situation when estimating train safety in crosswind with uniform wind. The influence law of aerodynamic characteristics affected by cross winds speed, wind direction and driving speed is described by cubic polynomial function, and the influence on head train is the most obvious. The relationship between aerodynamic drag coefficient, wind speed and wind direction can be described by dimensionless comprehensive formulae; for different train consists, aerodynamic performances of head train are almost same, so for the head car of a train that consists of more than three cars, the aerodynamic safety can be estimated in a certain extent, based on the analyses on a train that consists of three cars. The aerodynamic loads of pantographs and bogie account for10～20%of each train, so it should not be ignored;2. Flow field around high-speed train and transient behavior of the aerodynamic characteristics in constant wind field were simulated by Detached Eddy Simulation, and the unsteady property was analyzed. The results show that, in steady inlet flow field, there are separated vortexes with different intensities and geometric dimensions that change and pulse randomly with time on the leeward side and wake region of train; the time-averaged value of unsteady aerodynamic load value of each car is almost the same with that calculated in whole-field steady flow, while the peak value of transient load is higher than the time-averaged value; the maximum peak values of amplitude frequency spectrum and power spectrum are not same, but they are concentrated in0-4Hz, which is in the range of inherent frequency of some train parts. For head car, the range of distribution frequency of lateral force and overturning moment is large, it has a wide range of frequency coupling with the train itself, and the aerodynamic safety is poor in crosswind. The frequency that corresponded to maximum peak values of power spectrum of aerodynamic load on bogies are different, but they are concentrated in0.5～3.5Hz.3. The aerodynamic performance of high-speed train passing by in open air, the influence of crosswind on aerodynamic performance of meeting trains, and the influence of simplification of train model on the result of meeting trains simulation were analyzed based on moving mesh. The results show that for meeting trains at same speed, pressure pulse is basically proportional to the speed; for meeting trains at different speed, pressure pulse is effected by the ratio between the two speed, pressure pulse of lower speed train is higher than that of higher speed train; for passing trains in crosswind, pressure pulse is higher than that without crosswind, and pressure of every point on the leeward side is higher than that on the upwind, crosswind increases the danger of trains passing by, but the danger level of leeward train and upwind train are different. Aerodynamic performances of trains passing by in different road conditions were compared. Pressure wave and aerodynamic coefficient of meeting trains simulated with real model are higher than that with simplified model. In conditions of crosswind and non-crosswind, there were greater differences in pressure wave and aerodynamic force coefficient of meeting trains simulated with simplified model and real model, the difference of pressure wave amplitude can be one time higher, and the difference of aerodynamic force coefficient can be3～4times higher, and generally that with real model is higher.4. Influence of crosswind velocity and driving velocity on wheel-rail dynamic performance of high-speed train was studied based on multi-body dynamics simulation. The results show that crosswind and driving velocity are most influential parameters on derailment coefficient and wheel load reduction rate of head car, and the derailment coefficient and reduction rate of wheel load of head car are the largest among the three cars; the maximum values of derailment coefficient on the leeward side of head car and wheel load reduction rate on the windward side of head car increase obviously with the increase of wind velocity; and these dynamic performance parameter values increase with the increasing number of cars that compose a train. For the CRH high-speed train, derailment coefficient is only needed as safety evaluation criterion when track spectrum of Beijing-Tianjin railway line is employed; while wheel unloading rate should be added for safety evaluation criteria when track spectrum of German railways is employed. In addition, increasing random aerodynamic load in simulation was realized in the research.5. Safety control method of high-speed train in crosswind was studied. Security domain for train of running speed at different crosswind speed, namely speed limit of running train, was analyzed based on aerodynamics and wheel-rail dynamics, and the limited train speed was given; a new wind-proof device that ventilated with double-layer chamber was designed, and it is proofed of good comprehensive properties by simulating and analyzing the ability of keeping out the wind and wind self-resistance. Meanwhile, A new active-control method in which boundary layer separation is controlled through suction to decrease crosswind aerodynamic load on train is proposed, the action principle and effect were analyzed and proofed, which is a new way provided to improve crosswind safety of train.