Study On Transient Aerodynamic Characteristics Of Dynamic Swing Angle Overtaking

With the rapid development of high speed road network and the speeding pace of life,the overtaking around the curve or straight line on the highway have become a normal phenomenon.The increasing in vehicle speed,the aerodynamic force increases,the high speed driving control becomes complex,and the variation of aerodynamic force also will lead to vehicle yaw and lateral displacement,increased the high-speed driving psychological panic,these factors increase the risk of high-speed driving.Because overtaking is a special driving condition,in particular,the vehicle body motion trajectory and vehicle swing angle change with time,which is called the “dynamic swing angle overtaking ".With existing wind tunnel conditions,this special driving condition can not be tested,the numerical calculation method based on the finite volume method can not accurately simulate these real driving conditions yet.In recent years,the lattice Boltzmann method of molecular motion theory has developed rapidly,space discretization will not be subject to grid constraints,provides the simulation condition for overtaking and overtaking simulation.In this paper,firstly,the lattice Boltzmann method is used to carry out the simulation of the straight overtaking calculation process,and the results are verified with the experimental data and the previous research results,which prove the stability and reliability of the method.On the basis of this,the aerodynamic performance simulation of two kinds driving conditions are carried out,and the trend of overtaking aerodynamic force and regional dangerous to overtake are studied too.Through the establishment of real vehicle multi-body dynamics model of two overtaking condition of,the influence of aerodynamic side force on vehicle handling and stability are studied.Then,the optimization of vehicle body modeling and additional device improvement measures are put forward,and the aerodynamic characteristics of high speed driving are optimized.The details are as follows:1.Study on the current domestic and foreign research status of the automobile aerodynamic characteristics of vehicle handling stability,clarifies the purpose and significance of this research,proposed the research content and technical route.2.Describes the basic principle and theory of lattice Boltzmann method equation,boundary treatment scheme,lattice model and embedding different turbulence models of lattice Boltzmann method,combined with the pendulum angle characteristics of overtaking,determine the boundary conditions and the simulation program.3.According to the simulation scheme of a real gas model of lattice Boltzmann method of dynamic resistance calculation based on the comparison of wind tunnel test,the error is 0.827%,the accuracy of which is verified.On this basis,overtaking condition calculation results is consistent with the results of predecessors,the stability of the method is illustrated.4.According to the actual state of motion during the overtaking process,the overtaking and corner overtaking moving track is designed,Then,the dynamic swing angle overtaking and corner overtaking are simulated respectively,obtained under two conditions of aerodynamic curves of lateral force changes: the results show that in the overtaking and overtaking process in the lateral force coefficient changes,cosine curve.Under two kinds of conditions,the lateral force coefficient of the car gets to the peak negative value at the distance of the length ratio coefficient D/L=0 and 3.5,overtaking car maximum peak side force coefficient is greater than the corner overtaking,at the length ratio coefficient D/L=-0.285.5.Aiming at the particularity of overtaking,constructed a real car multi-body dynamics model of overtaking.Then,the influence of aerodynamic side force on the vehicle handling stability is studied,compared without considering the aerodynamic side force effect.The lateral displacement of the moving track of the vehicle with the change of aerodynamic force is considered,and the maximum offset is 180.195mm;If the return operation delay 0.25 s,the side are partial to reach 1520.0637 mm.6.On the basis of this,the optimization and improvement of vehicle body shape optimization and additional device are carried out,the lateral force coefficient models of overtaking risk area decreased by 31.25%,overtaking the body lateral offset is reduced by 8.35%.