Study On The Influences Of The Simplified Forms Of External Windshield Capsule Of The High-speed Train On Simulation Results Of Tunnel Aerodynamic Effects

The high-speed train plays an important role in the transportation industry because of high efficiency,convenience and economic advantages.However,with the improvement of the speed,the aerodynamic effects of tunnel induced by the high-speed train have caused more and more attention.At the same time,the car-gap as one of the important components of the vehicle,the research of aerodynamic characteristics of the windshield is also a top priority.The simplification of the windshield model is a crucial step in the study,because when using the appropriate aerodynamic model,not only can achieve accurate simulation results,but also can save a lot of computational resources.The windshields of the train tends to adopt a larger simplification method,that is,the opening end and the internal cavity of the windshield capsule are ignored on the basis of only considering the outer annular shape.However,whether it is a fully enclosed or semi-enclosed external windshield,the influences of the simplified forms of the windshields on the numerical simulation results of the tunnel aerodynamic effects of the high-speed train currently lack systematic results.Taking this as the background,I will choose the high-speed railway single-hole double-track tunnel with a clearance area of 100m~2 and a certain type of EMU with a speed of350km/h as the researching objects,the three-dimensional unsteady viscous compressible Navier-Stokes and SST k-ωtwo-equation turbulence model are adopted.The overset mesh method of Star-CCM+is used to simulate the aerodynamic effects of two different forms of the windshields.The calculation model of the paper is a full-size 8 cars,with the pantograph regions and the bogies.The windshields have two simplified forms,one retains the opening port,the inner cavity and the holes of the inner wall,the other only retains the annular shape.Firstly,I will use the unstructured hybrid grid to discretize the computational areas.The grid design method can meet the requirement of calculation accuracy through independence verification.At the same time,through the real data of the experiment,the method is verified.Secondly,by analyzing the pressure and velocity distribution cloud maps,the pressure wave formation mechanism,variation characteristics of the single train entering the tunnel and the influences of two shapes of the windshields on the pressure distribution are obtained.By drawing the velocity vector diagram of the internal flow field,we find that the gap at the bottom of the windshield is the“inlet”,and the gaps between the two sides are“outlet”.The air entering the interior of the car-gap will produce some large fluid vortexes.Because of the inner holes and the cavity,part of the gas of the form 1 flows from the inner cavity to the end.Duing to the differences of air flow,the windward side and the leeward side of windshield-1,windshield-4 and windshield-7 are selected to analyse pressure lines.Considering the pressure wave as a key parameter for the analysis of the aerodynamic performance of the train,the pressure monitoring points at different positions on the surface of the head vehicle,the intermediate vehicle(vehicle-5)and the tail car,and the windshield-1,windshield-4,and windshield-7 are selected to analyse the influences.It is concluded that the simplified forms of the windshields have no significant influences on the pressure changes of the walls of the vehicle bodies and the ends of the windshields in the entire time.Finally,I will analyse the aerodynamic drag,lateral and lift forces of the vehicles and windshields.There are a few influences on the windshields between two simplified forms,the influences on the whole vehicle can be neglected nearly.For the aerodynamic lateral force,the two simplified forms of the windshields have few differences before the tail entering the tunnel,when the train completely goes into the tunnel,the differences of the lateral force are obvious,the positive and negative peaks of the lateral force of the form 1 are larger than the other.For the aerodynamic lift,the two simplified forms of the windshields have less influences on themselves,but can change the characteristics of the aerodynamic lift of the whole train.