Identification Of Key Parameters And Wind Environment Adaptability Analysis Of Large Passenger Car Wind Resistance Brake Wing Plate

With the increasing of the speed,the kinetic energy of the road bus increases with the square of the speed,but the braking performance of the wheel and the ground friction will be restricted by the adhesion,so the braking accidents of large buses occur from time to time.Drawing on the application of wind brake in train,in order to improve the braking performance,wind brake has become a choice in bus.By opening the wings to increase the aerodynamic resistance and aerodynamic lift of the passenger car,the braking performance can be improved and the passenger car can show better braking performance at high speed.In this paper,the aerodynamic characteristics of the air drag brake bus in the process of high speed emergency braking are studied.Combined with the aerodynamic and multi-body dynamics theory,the combination of wing profile parameters is selected to make the best braking performance,and the braking characteristics of the air drag brake bus under different cross-wind speeds are analyzed.The research contents mainly include:First,in order to ensure the accuracy and reliability of the numerical simulation results in this paper,the simulation model used in this paper needs to be verified by referring to experimental data.For the passenger car aerodynamics model,Ahmed model with a large number of experimental data and similar model shape and outflow field to the passenger car model in this paper was selected as the verification model,and Open FOAM software was used to conduct mesh classification for it.In order to optimize the numerical simulation strategy,the orthogonal test of grid size,turbulence model,pressure-velocity coupling equation and spatial discrete format was carried out by using₉L（3⁴）orthogonal table.Finally,the numerical simulation strategy with the highest simulation accuracy was obtained.Then the CFD uncertainty analysis of the simulation results verifies the reliability of the simulation model.The FLUENT dynamic grid technology used in unsteady simulation is verified by reference to wind tunnel experimental data.In order to analyze the influence of wing aerodynamic parameters on the aerodynamic performance of bus.In this paper,the relationship between vehicle speed,opening Angle of the wing,installation position of the wing,height of the wing and aerodynamic coefficient is studied by using control variable method and orthogonal test method.It is found that the two methods reach the same conclusion,that is,the optimal configuration parameters of the wing are:the mounting position x=10 m,the maximum opening Angleθ=80°,and the height h=1 m.According to the results of range analysis and variance analysis,the primary and secondary order of influence on aerodynamic coefficient is as follows:the mounting position of the wing>the maximum opening Angle of the wing>the height of the wing>the speed of the vehicle.According to the optimal shape parameters of the wing,a new finite element model of aerodynamic brake bus is established for unsteady simulation.The cross wind speed was divided into five working conditions with a gradient of 5 m/s from 0 m/s to 20 m/s,and the simulation results were combined to analyze the influence of wind environment on the braking characteristics of the aerodynamic brake bus.The simulation results show that when the cross wind speed is small（wind speed is less than 10 m/s）,the braking performance is better than that when there is no cross wind.When the cross wind speed continues to increase,the braking performance will continue to decline,indicating that the excessive cross wind speed will affect the braking performance of the brake wing.When the cross-wind speed is larger（the wind speed is more than 15 m/s）,the braking safety and comfort of the wind-brake passenger car are also greatly challenged,so we should try to avoid using the wind-brake wing plate when the cross-wind speed is too large.