Numerical Simulation On Characteristics Of Unsteady Flow Around High-speed Train In Open Air

As train speed constantly increases, the aerodynamic effect of flow around train becomes more and more important. In particular, when train speed reaches above 300km/h, the aerodynamic drag accounts for over 80% of the total resistance. The flow around a train running at high speed is unsteady in nature. Especially when a train running at high speed in an open line encounters crosswind, the aerodynamic characteristics and pressure distribution on train surface are significantly different from that under the case of no crosswind. The external flow around the high-speed train changes more violently, and the flow structure is more complex. Thus the unsteady characteristics of air flow are particularly prominent in the zone of train tail and the chassis at the bottom of the train. The resulting unsteady aerodynamic loading acting on the surface of the train tends to make the train vibrate while running, and largely impacts the stability, safety and riding comfort of the train. Therefore, it is necessary to carry out an intensive study on unsteady characteristics of external flow around trains running at high speed in an open line.The present work was planned to analyze the unsteady characteristics of external flow around four-car model of 350 km CEMU for cases with and without crosswind in an open line with a non-scale model and its components and parts via numerical simulation. The aerodynamic loading, air pressure distribution on surface and flow structure around the train and that of each compartment and of the whole unit was analyzed.First of all, RANS, URANS and DES were adopted for numerical simulation of flow around a circular cylinder. The results were compared with the values in literatures. The influence of the vortices periodic formation, development and shedding of the flow structure around a circular cylinder, i.e. Karman Vortex Street in wakeof the circular cylinder, were analyzed. Thus the feasibility of the DES method was verified again.Secondly, comparison study was conducted to verify the numerical simulation calculation, in order to check the reliability of the mesh generation method and the numerical method. For 1:8 scale model of CRH380 A wind tunnel, RANS, URANS and DES were employed for comparison verification. The numerical results were compared with the test results for both the cases of with and without crosswind. The differences of above three calculation methods were analyzed, in order to figure out a reliable numerical calculation method and mesh setting scheme.At last, the unsteady characteristics of external flow qround a 350 km CEMU for cases with and without crosswind in an open line were studied with a non-scaled model. The unsteady characteristics and aerodynamic loading distribution of external flow around the CEMU and its key parts were analyzed.In a word, the unsteady characteristics of external flow around the 350 km CEMU were studied focusing on the areas near the train where the unsteady characteristics were prominent. The influence of external flow of a train on the aerodynamic performance of the train and the flow distribution law were figured out, which is of certain practical significance and reference value.