Influence Of Velocity On Transient Aerodynamic Characteristics Of Plural Vehicle

The aerodynamic stability in cars is the premise of high-speed, safe driving. Complex terrains, such as traffic routes, tunnels, bridges and roadbed, will cause artificial gust, which will impose an additional force of vehicles, causing traffic lateral force and yaw moment changes. When the two cars have overtaking or crossing process, the role of the lateral force can not be ignored. Instantaneous aerodynamic changes often lead to changes in running track, or even an accident. The velocity between the two vehicles is the major security factors in this course. The high-speed driving conditions of plural vehicles can be divided into overtaking, crossing and platoon. This paper studies on the overtaking and crossing process in the view of automotive aerodynamics in order to find transient aerodynamic characteristics and its effect on the stability of high-speed plural vehicles. The discovery is of great practical significance. It can provide drivers with a reference of reasonable speed in their similar cases.The moving mesh offered by commercial computational fluid dynamics (CFD) software Fluent was adopted to realize transient aerodynamic characteristics numerical simulation during the overtaking and crossing process. Through the calculation of the six conditions in different speed, the analysis of static field of aerodynamic flow and pressure field of model surface, the rule of the transient aerodynamic characteristics' changes of speed was discovered, and appropriate suggestion for the driver was offered.The results show that:In the whole process,the aerodynamic coefficient of vehicles has similarity sine curve changes. The relative velocity has a little influence on the overtaking vehicle, but much influence on the overtaken vehicle during the overtaking process. With the increase of the relative velocity, the variations of side force coefficient of the overtaken vehicle will increase linearly. Vehicles with faster velocities have more transient aerodynamic influence on each other during crossing process.