Approaches And Dynamic Performances Of High-Speed Train Fluid-Structure

Safety is the spririt of railway transportation and the most important premise and guarantee to speed up. In the field of traditional train aerodynamics, the change of running attitude of train by the action of aerodynamic forces is neglected. The excitation forces are added to the vehicle dynamics and the running safety is analyzed. In fact, the high-speed train aerodynamics and vehicle-track dynamics, which are inseparable parts of high-speed transportation system, are mutually coupled and influenced. The running attitude of train would be changed by the action of aerodynamic forces and then the running attitude affects the flow field around train. Therefore, the aerodynamic forces of train would change and the train system would be in a particular coupling vibration state under such mutual feedback. High-speed train fluid-structure dynamics considering the change of running attitude of train by the action of fluid forces can reflect the essence of high-speed train system impersonally.For the running safety issue of high-speed train by the action of aerodynamic forces, the dynamic model of high-speed train fluid-structure was established. Based on the model and approaches, the running safety of high-speed train was analyzed under crossind, wind shear and sandstorm environment. In the computational fluid dynamic model, the Navier-Stokes equation and k-e two equations turbulence model were adopted; the Finite Volume Method (FVM) and moving mesh technique were used. The moving boundary between train and air was dealed with arbitrary Lagrangian-Eulerian (ALE) method.With the established dynamic model of high-speed train fluid-structure, a co-simulation approach of high-speed train fluid-structure interaction was presented based on the vehicle dynamics software Simpack and computational fluid dynamics software Fluent. The co-simulation platform combined with Fluent and simpack was set up to exert their advantages in separate platform and eliminate the limit with single platform in simulation. Besides, an inserted co-simulation approach of high-speed train fluid-structure interaction was presented. The datum communication of fluid solver and structure solver was avoided by inserting the program of vehicle-track coupling dynamics into the fluid dynamics program. Therefore, the calculation efficiency was improved. Moreover, a co-simulation approach with relaxation factor of high-speed train fluid-structure interaction was presented. By introducing the relaxation factor about load boundary of fluid-structure interface, the fluctuation and convergence of aerodynamic forces were improved. When relaxation factor equaled0.5, the fluctuation and convergence of aerodynamic forces were relative smaller.For the running safety issue of high-speed train under crosswind environment, two fast and high-efficiency equilibrium state methods were presented. The differences in aerodynamic forces and safety indexes calculated with equilibrium state method, the alternative co-simulation and off-line simulation were compared. It is shown that there is little difference in results calculated with equilibrium state method and alternative co-simulation; however, the calculation efficiency of asynchronous equilibrium state method is highest in all co-simulations. After considering the interaction effect, the aerodynamic forces and safety indexes of head coach were become larger. That’s mean the running safety of high-speed train became worse. In the crosswind environment, most of vortexes were shedding from the surface of train and a few vortexes were generated by extruding between two main vortexes. Besides, with the decrease of yaw angle, the number of main vortexes shedding from train lee side decreased and the first main vortex was shedding more far from the nose of head coach. When the running speed of train is more than300km/h, the wheel unloading and wheelset lateral force are chosen as the safety evaluation indexes, which would get the minimum wind velocity allowed maximumly; when the running speed of train is less than250km/h, the wheelset lateral force is chosen as the safety evaluation index, which would get the minimum wind velocity allowed maximumly.For the running safety issue of high-speed train under typical wind shear environment, dynamics of high-speed train passing the windbreak in crosswind were numerical simulated based on the train aerodynamics and train dynamics. The aerodynamic forces and dynamic responses of high-speed passing the windbreak were analyzed. The dynamics on crosswind velocity were analyzed. Besides, a kind type of windbreak with buffer equipment was advanced, which could improve the safety and comfort effectively when the high-speed train passed the windbreak. For the issue of linear wind shear with a steady region, a fast approach of high-speed train fluid-structure dynamic, namely quasi-steady approach was presented. Based on that approach, the dynamic performances of high-speed train were analyzed under different wind shear environment. It found that the region of safety running speed under wind shear environment is smaller than that under traditional crosswind environment, viz. the running safety becomes worse under wind shear environment.For the running safety issue of high-speed train under sandstorm environment, a half interaction approach was present with the consideration of calculation effencicy and fluid-structure interaction effect. Based on that approach, the dynamic performances of high-speed train were analyzed under different sandstorm environment. It is concluded that the safety indexes become worse with the incremental of train speed and the intensity of sandstorm. Wheelset lateral force, derailment coefficient and wheel unloading are beyond the allowed values in some cases, besides, the wheel rail vertical force is relative hard to go beyond the allowed values.In the sandstorm environment, when the running speed of train is350km/h, the allowed crosswind velocity is only9.08m/s; when the running speed of train is300km/h, the allowed crosswind velocity is15m/s. Those results should be attracted some relational department’s attention.