| High-speed trains are the core equipment of high-speed railways.When the train is running at high speed,the interaction between the surrounding air and the train intensifies and the turbulent flow field with a very complex flow structure is formed around the train,which in turn causes a series of aerodynamic problems and directly affects the safety,stability and comfort of the passengers in train operation.There is a direct correlation between the external shape of the train and its aerodynamic performance.The head car,as an important component of the high-speed train,needs not only to meet visual aesthetic criteria but also to have good aerodynamic performance.For these reasons,the following research is carried out in the thesis:(1)Reasonable improvement of the head shape bionic design process for high-speed trains.Based on the full consideration of different living environments and speeds,the peregrine falcon,albatross,crocodile and barracuda are selected as the bionic objects,and the design of the hand-drawn scheme of the bionic head shape is completed by extracting the characteristic lines of the organism’s head under the premise of setting the relevant dimensional constraints of the train head reasonably.The Non-Uniform Rational B-Splines(NURBS)method is used to establish the calculation models for each of the four bionic trains.(2)Numerical calculations of aerodynamic performance related to bionic trains.Computational Fluid Dynamics(CFD)is used to simulate the aerodynamic performance of the four bionic trains in open air single car and crosswind conditions respectively.The results show that the albatross train is the best and the crocodile train is the worst in terms of aerodynamic drag in open air,with a 30.9% difference in the aerodynamic drag coefficient.Under crosswind conditions,the side force coefficient of the albatross train is the largest,while that of the crocodile train is the smallest,with a difference of 55.1%,moreover,the side force coefficients between the four bionic trains are the largest for the head car,lower for the middle car and the smallest for the tail car.At the same time,when the running speed is the same,the cross wind makes the aerodynamic drag of the head car decrease and the aerodynamic drag of the middle car and the tail car increase.(3)Multi-objective optimization of the aerodynamic performance of bionic trains under crosswind conditions.In order to fully exploit the aerodynamic performance potential of the bionic train under crosswind conditions,based on a comprehensive analysis of the specific characteristics of the four bionic head types and the advantages and disadvantages of the aerodynamic performance indexes of the train under crosswind conditions,the single-arch form of the barracuda train and the double-arch form of the albatross train are selected as the optimization objects,and parametric models of the two trains are established.A NonDominated Sorting Genetic Algorithms(NSGA-Ⅱ)is used to optimize the head car lateral force and the aerodynamic drag of the whole car as the optimization objectives.The degree of influence of multiple optimization design variables on the optimization objectives is explored for both models,and the Pareto optimal solution fronts for each of the two train head shapes are obtained.Compared with the original head shape,the head car air lateral force and the whole car aerodynamic drag of the barracuda train are reduced by a maximum of 3.87% and3.23% respectively;the two optimization objectives of the albatross train are reduced by a maximum of 2.60% and 4.20% respectively.(4)Structural analysis of the train surface pressure and leeward side flow field under crosswind conditions.The multi-objective optimized barracuda and albatross trains are studied respectively,and the distribution of pressure coefficients in the horizontal and cross sections of the car bodies of the two trains are illustrated in detail under crosswind conditions.The results show that most areas on the windward side of the two optimized trains are positively pressure,while most areas on the leeward side are negatively pressure,but the pressure distribution in the streamlined sections of the head and tail cars,and at the transition between the roof and the side walls,is significantly different from that of the car body parts.At the same time,as the vortex structure on the leeward side of the car body causes the whole flow field to exhibit strongly non-constant characteristics,the non-constant characteristics of the flow field on the leeward side are analyzed using the Q-criterion and vortex volume methods.The results show that although the location of vortex generation and development patterns on the leeward side of the two optimized trains are similar,there are differences in the location of the vortex from the car body and in the intensity of the vortex in cross sections at the same location. |
