Research On The Brakong Principle Of Air Resistance Of High-speed Trains And The Mechanism Of Flow Field Deterioation

As one of the key technologies of the vehicle,the braking system plays a vital role in guaranteeing the high-speed,safe and comfortable operation of the vehicle.With the rapid development of high-speed railways and the continuous improvement of vehicle running speed,as well as the development of high-speed,intelligent and green railway vehicle equipment,the development of a new generation of high-speed maglev vehicles with a speed of 600kilometers per hour,and the development of low-vacuum pipeline maglev transportation technology,there is a need for braking technology.higher requirements.The kinetic energy of the vehicle increases with the square of the vehicle speed.Under the condition of a certain braking distance,the braking power of the vehicle is a cubic function of the vehicle speed;The coefficient will also decrease significantly with the increase of vehicle speed;high vehicle speed will also bring severe challenges to the temperature rise and thermal stress of the disc brake vehicle;and the air resistance is proportional to the square of the vehicle speed.Therefore,in order to increase the braking force of the vehicle,the aerodynamic braking of high-speed trains has become a better choice.This paper firstly determines the basic aerodynamic characteristic parameters of the aerodynamic brake train according to the literature research,and establishes a three-dimensional model with a high degree of reduction.Then,based on the FLUENT simulation platform,according to the flow field characteristics of vehicle aerodynamic braking,researches on grid density independence,time step independence,and turbulence model adaptability are carried out.The flow field simulation method with flow,multi-vortex and strong unsteady characteristics is finally determined.The spatial discrete format is QUICK,the pressure-velocity coupling equation is selected as the SIMPLEC algorithm,and the turbulence model is selected as SST k-omega.The influence of the aerodynamic parameters of the wing plate on the aerodynamic characteristics of the train is analyzed.First,using the control variable method,the model of the head car+1.5 middle car was selected,and the single-parameter analysis was carried out on the shape(aspect ratio),area,maximum opening angle,installation position and quantity of the fender respectively.Then,using the orthogonal experiment method,L9(3~3)orthogonal test was carried out on the three key parameters of area,angle and quantity,and the range analysis and variance analysis were carried out using the aerodynamic drag coefficients corresponding to 9 groups of working conditions,and the experimental working condition was determined.The optimal combination of wing parameters and the sensitivity of each parameter.The dynamic grid technology is used to simulate the unsteady aerodynamic characteristics of the train wing plate braking process,and the flow field is visualized from the pressure distribution,vortex structure,velocity streamline and other aspects,and the whole process of the wing plate braking process is proved.The evolution law of the traffic flow field;the aerodynamic load spectrum within 2s of the opening process of the wing plate is analyzed,and the interference characteristics of the wing plate on the aerodynamic force of the vehicle are verified.The study found that the wing plate can increase the resistance of the vehicle by up to200%,but due to the deterioration of the flow field of the vehicle by the wing plate,while the wing plate provides braking resistance,it will also increase the lift of the vehicle body,which is very harmful to the train.threat to the vertical stability.The study on the deterioration mechanism of ambient wind on the flow field of the wing-plate braked train is introduced,and then the aerodynamic load obtained by FLUENT is imported into the SIMPACK calculation model,and the system dynamics calculation of the train is carried out,and the safety of the whole vehicle operation due to the opening of the wing plate under different cross winds is obtained.The influence of sexual indicators.The research shows that the rapid opening of the wing plate can provide a large braking force and improve the emergency braking performance of the train on the one hand;It deteriorates the flow field in the middle and upper parts of the car body,and threatens the running safety of the train under cross-wind conditions.On the whole,with the increase of the crosswind wind speed,the derailment coefficient and wheel load reduction rate of each vehicle showed an upward trend,and even derailment and overturning occurred in severe cases;in the wind environment,the safety index of the van to the leading vehicle deteriorated.The most serious,as long as the safety of the opening process of the front wing panel is ensured,the safety of the whole vehicle can be guaranteed.