Effect And Optimization Of Aerodynamic Lift On Vehicle Aerodynamic Driving Stability

As the aerodynamic lift is proportional to the square of the speed,the aerodynamic lift on the vehicle body will increase rapidly after the speed of 70 km/h,which will seriously affect the stability of the vehicle power system.For example,some vehicles "floating" at high speed,the driver loses the sense of road surface,and even the vehicle is out of control resulting in a traffic accident in serious cases.Therefore,exploring the influence of aerodynamic lift on the stability of vehicles at high speeds has increasingly become a hot issue in automotive aerodynamics research.However,most of the current research is basically on the optimization control of aerodynamic lift using an additional device in the aerodynamic category of automobiles,and it cannot truly reflect the response of the aerodynamic lift to the dynamic system of the vehicle during driving.In view of the above problems,this paper builds a systematic dynamics calculation model of the whole vehicle on the basis of the test of wind tunnel experiment,carries on the multi-working condition calculation of high-speed driving state,takes the three dynamic parameters of lateral displacement,lateral acceleration and yaw velocity as the stability response evaluation parameters.The vehicle system dynamics of the vehicle system under the condition of calculating and the front and rear axles aerodynamic lift are studied.Constructs the dynamic model of aerodynamic lift and body dynamic parameters.Finally,in order to improve the aerodynamic stability,the optimization design of sopiler is carried out by applying multi-island genetic algorithm for the actual model.The model,method and theory established have important guiding significance and engineering application value to improve the design level of automobile body.The specific research contents are as follows.1.In order to analyze the aerodynamic lift characteristics of the model,an aerodynamic simulation experiment model was established.The HD-2 wind tunnel model experiments were carried out,and the reliability of numerical simulation scheme and results were verified.2.The system dynamics model was established by using the three-dimensional coordinates of the suspension hard points and the parameters of the vehicle.The sensitivity and robustness of the model were verified by the interaction feedback method.3.In order to research the stability of vehicle dynamics system under the influence of aerodynamic lift,the three operating conditions simulation of stable steering,changing path and emergency barrier avoidance were carried out by using the established systematic dynamics model.The vehicle driving stability in the case of having aerodynamic lift or not,different speed and front and rear axles lift decomposition were studied by quantitative analysis of the three indicators of lateral displacement,lateral acceleration and yaw velocity.After the aerodynamic lift loaded,the maximum lateral acceleration of the vehicle under stable steering conditions is reduced by 6%and the maximum yaw velocity is reduced by 4%.At the same time,the vehicle’s turning radius becomes larger,the handling and the stability becomes worse.4.Aiming at the three common forms of instability,side-slip,roll over and pitching,the law of force response of aerodynamic lift to vehicle in the critical state of instability is studied.The corresponding critical state mechanical model is constructed,and the analysis of the high-speed driving stability of vehicles is carried out by applying the critical instability mechanics model.5.In order to prevent high-speed instability caused by excessive aerodynamic lift,with the goal of improving high-speed stability,the critical model is used to construct the optimization strategy,which is to reduce the aerodynamic lift of the vehicle.The aerodynamic stability of the vehicle is optimally controlled through the additional device of the spoiler.In the optimization,the interaction effect analysis of spoiler shape parameters is carried out by using parametric modeling and experimental design.The optimal spoiler angle of attack is 25 degrees and the optimal spoiler length is 80mm.The optimized vehicle’s lateral acceleration maximum is increased by 0.083 g and the maximum yaw velocity is increased by 1.25 degrees/s,significant improvement in high-speed stability.