Aerodynamics Research On High Speed Train Passing Each Other

With the rapid development of high-speed railway in China, aerodynamics phenomena caused by high-speed train is also emerging gradually, especially when two trains pass by each other. The strong squeezed air flowing between the two vehicles shall produce a strong transient pressure impact on the surface of two trains, which may break the glass into pieces or suck off the windowpanes of the trains. If the pressure wave spreads to the poor air-proof compartment, it possibly would result in disconfortable symptoms on passengers such as tinnitus, dizziness etc. In addition, each carriage will also receive the alternating aerodynamic force and moment impulsion, which may lead to the horizontal or vertical vibration and hunting motion. This will not only deteriorate the wheel track abrasion and greatly affect the safety and smooth operation for trains, but result in train derailment, overturning and other heavy incidents. However, the variation law of pressure wave, dynamic forces and moments when two high-speed train pass by each other in the open air, as well as the specific formula among the following influencing factors such as trains speed, train external dimensions, track spacing and vehicle spacing etc. are still lack. Passing by the noise barrier with a high speed, the train would generate prodigious air pressure fluctuation on the sound barrier, which may tremendously affect the fatigue life of noise barrier. Once the noise barrier become invalid due to intensity or fatigue damage, it is likely to endanger traffic safety operation. In order to meet the requirements of high-speed train safety operation, comfort, low energy consumption etc., aerodynamic characteristics must be intensively studied the process of two trains passing by each other.Based on 3D viscous transient compressible Navier-Stokes equations andκ-εturbulent model, a simulation analysis on aerodynamic pressure wave, force and moment acting on train when two high-speed trains passing by each other was investigated by the technology of moving grids and finite volume method. The pressure on train surface and the aerodynamic force's changing process was analyzed when two rains passing through each other. The law of pressure wave externally distributed, as well as similarities and differences of aerodynamic forces and moments on each carriage were obtained. By calculating the pressure wave and aerodynamic forces under 6 kinds of track space when the train passing under static condition, with the same speed or different speed, a method to study the pressure wave and aerodynamic forces is found when the trains pass through at any speed and any distance of track spacing in the open air, the whole set quantitative formulas of pressure wave and aerodynamic forces about the train's speed, track spacing or vehicle spacing were obtained. Furthermore,3 types and 2 kinds of heights of noise barrier structures and aerodynamic were also studied when two train pass through under the same speeds. All of these researches can provide reference for the design of high-speed railway and train.The results indicated as followed:(1) the pressure wave's shape and peak value of train passing depand on the position. The absolute pressure on head and tail of the train is much bigger than pressure on the middle of the train, while the pressure wave amplitude is smaller. In the identical lateral section, the peak and amplitude of pressure wave on the crossing side surface is much bigger than pressure wave on the top, bottom and the opposite crossing side.(2) The peak or amplitude value of pressure wave and aerodynamic forces related with the speed of the passing trains, and set up the functional relationship with the ratio of relative velocity-the ratio of passing train speed and relative velocity Passing by each other at any velocity, the pressure wave peak or the peak-to-peak value and the relative velocity ratio is 6 power polynomial relations; aerodynamic drag coefficient and relative velocity ratio is 4 power polynomial relations; aerodynamic side force coefficient and the relative velocity ratio is quadratic function; aerodynamic lift force, rolling,pitching and yawing moment coefficient and the relative velocity ratio is cubic function.(3) Pressure wave, aerodynamic forces and moments is the negative exponent relation with the track spacing or the vehicle spacing.(4) With the relative velocity ratio decreasing, the tail wave of the pressure and aerodynamics forces moved down comparatively to the head wave. So in the un-uniform velocity intersection, the extend of harm caused by aerodynamic characteristics under the circumstance that the train passed the tail part of low speed train is much severer than that passed by the head part of the low speed train.(5) The time interval of the aerodynamic drag peak-to-peak is the shortest and fiercest, successively, the pitching and yawing moment, while side force, lift force and rolling moment have the most ease.(6) When two trains pass by each other, aerodynamic pitching moment, yawing moment which appear 6 peaks change much fiercer and dangerous than the aerodynamic side force, lift force and rolling moment which appear 4 peaks.(7) Aerodynamic force acting on unit length noise barrier of invert L type is the maximum one and that of upright type is the minimum. The aerodynamic forces acting on different type of noise barriers are all quadratic functions to the passing train speed. Aerodynamic force acting on the noise barrier increases with the height of the noise barrier.