Principle And Improvement Research About Attachment Devices Affecting Aerodynamic Lift Of Vehicles

Vehicles are often “waving” at high speed, which enabling drivers to lose the roadfeel and the steering system being sluggish response. Even driver would lose thecontrol of the vehicle completely, if it “waving” severely. The direct reason for“waving” is that aerodynamic lift hold up the vehicle perpendicular to the groundovercoming the gravity which making the adhesiveness worse. So the aerodynamic liftcoefficient is very important in the process of automotive aerodynamics design whichinfluencing stability and safety of vehicle. With the higher aerodynamic lift coefficient,the wheels of car may lose some grip force on high speed, even a traffic accidentcaused. However the aerodynamic lift can be changed to negative lift by wellaerodynamic design. The higher the velocity increasing, the bigger negative liftincreases, which ensuring the high speed driving.The causes of aerodynamic lift were analyzed in this paper. Through the analysisof the flow field distribution, the influence factors of aerodynamic lift were researched.Aerodynamic attachment devices are designed to the improvement of aerodynamic lift.It’s engineering significant to improve the stability of high speed vehicle. Because ofthe advancement in modern computer technology and the continuous development ofturbulence theory, Computational Fluid Dynamics (CFD for short) began to widely beused in the development research of automotive aerodynamics. This paper is based onCFD simulation technology to analyze the impact mechanism of the car aerodynamiclift, and uses aerodynamic attachment devices to improve the aerodynamic lift of thevehicle.First of all, according to simulating the flow field of cylindrical,“Ground Effect”was researched which is an important influence factor of aerodynamic lift. A bluffbody was constructed to study. With CFD simulations by different ride height of thebluff body and angle of the diffuser, the regulation of ride height and angle to the liftforce was studied.Secondly, the bottom flow field of “ZhongQi” was improved base on “GroundEffect” theory. The bottom of underhood was sealed by a cover plate so that the speedof the airflow at the bottom can be increased and the pressure can be decreased.Consequently the lift force was reduced. With the improvement of adding lip, theairflow down underneath the car was reduced, so the lift force reduced. Thirdly, the diffuser of a sports car was analyzed and improved. A car modelwithout diffuser was compared to explain the role of the diffuser. In order to reduce thelift force, the diffuser was designed to three different forms: Expand work space，Withtriangle wing wall，and With spoiler. These programs all make the lift force reduced.The diffuser is more obvious improvement of the aerodynamic lift by adding thetriangle wing wall; spoiler and diffuser combination of programs with greater potentialfor the improvement of aerodynamic lift, but a slight increase in resistance, higherground clearance requirements.Finally, this paper introduces modem optimization algorithm to aerodynamicdesign. A variable rear spoiler was designed and optimized with genetic algorithmbased on approximate surrogate model, reducing the drag force and lift force of thevehicle. At high brake condition, the variable spoiler can provide larger negative lift asan “air brake”.