Numerical Study Of Vehicle Aerodynamic Performance During Complex Driving Condition

Aerodynamic characteristic is an important performance for vehicle. It directly influences the vehicle dynamic, fuel economy, comfortableness, control stability and safety characters. Chinese is a big country of Auto. With more and more vehicle driving on the road, the security incidents are also increasing. The control stability and safety characters are increasingly attracted people’s attention. The topography is variable. The vehicle driving condition is complex for the different road conditions. The influence of the increasing vehicle on the city road, coupled the traffic light, cause vehicle frequently acceleration and deceleration. The aerodynamic performance is complex during the complex driving conditions. And the influence of aerodynamic performance for vehicle control stability and safety is more significant. Therefore, recent years, people paid much more attention to the researches of vehicle aerodynamic performance.Currently, for the study of vehicle aerodynamic performance mainly are numerical simulation, wind tunnel test and road test. With the developing of computer and computation fluid dynamic(CFD) software, numerical simulation could reach highly accuracy on the simulation of vehicle aerodynamic performance. For the simple driving condition, such as line driving with constant speed, both numerical simulation and wind tunnel test could achieve. But for the complex driving condition, such as curve driving, wind tunnel test and road test show much more limitations, even they could not achieve this research. Numerical simulation shows absolute advantage in these fields.Based on the dynamic mesh technique and User Defined Functions(UDF) of Fluent software, this paper carry out simple secondary development for Fluent to achieve different driving conditions. Through this simulation method, the vehicle aerodynamic performance in complex driving condition has been studied.Firstly, the UDF program achieved the simulation of vehicle acceleration and deceleration driving condition. It re-appeared the vehicle aerodynamic performance in the process of acceleration, constant, then deceleration. The flow structure of vehicle and the pressure distribution are obtained.Then, the research method of Fluent dynamic mesh technique coupled UDF is applied in the line driving with constant speed driving condition. Compared the simulation results with wind tunnel test results to verify the research method is accurate and feasible. And then this research method is applied in the vehicle curve driving, simulate and analyze the changes of vehicle aerodynamic performance.At last, this research method is applied in multi vehicle of line meeting and curve meeting condition. Contrastive study the aerodynamic performance between vehicles line meeting and curve meeting, analyze the difference and the reasons.