Research On Vehicle Transient Aerodynamic During Overtaking

With the development of highway and the increase of cars, complex driving condition lead to more and more overtaking appear. As high-speed overtaking, the vehicle flow field interference between the vehicle will seriously affect the aerodynamic characteristics. It will greatly affect the vehicle handling stability and security, and even caused a traffic accident. Aerodynamic stability of high-speed vehicle is a guarantee of overtaking. The research of the aerodynamic characteristics of high-speed overtaking process has great practical significance.In this paper, CFD has been use on numerical simulation of the transient overtaking. And several discussions are made in this paper, such as dispersion method of transient term in turbulence models, numerical models using in CFD transient simulation computation, different lateral spacing overtaking routine are under consideration. And the relationship and changes of drag coefficient, lift coefficient and side force coefficient of both the passing vehicle and the passed vehicle has been obtained. At Last, by analysis the static pressure field, dynamic pressure field, velocity field and the model surface pressure field, the process of overtaking aerodynamic coefficient change has been explained.Through analysis several conclusion are made:1.In the whole passing process, the coefficient of drag, lift and side force are distribute like trigonometric function shape and changed dramatically as lateral spacing decreased.2.In the passing process, the aerodynamic force varies with the longitudinal relative position. When the front end of overtaking vehicle reaches the rear of overtaken vehicle, the side force coefficient and drag coefficient reach the maximum. When the front end of overtaking vehicle reaches the middle of overtaken vehicle, the side force coefficient and drag coefficient reach the maximum.3.For whole overtaking processes, the main reason of the aerodynamic drag coefficient changes is the mutual interference of the vehicles flow field. 4.In the whole passing processes, side forces are changing not only in amount but also in direction. The maximum occur on x / L=0.5 (x is the vertical distance between two vehicles, L is the vehicle width) and x / L=1.5, and direction change on x / L=0.