Numerical Simulation Of Transient Aerodynamic Characteristics Of Vehicle Driving In Curved Road

As one of the factors that significantly affect security and stability of vehicles, theaerodynamic characteristic, has also been paid more and more attention recently. The rapiddevelopment of modern automobile industry and transportation, enhancing the quantity andquality of vehicles, complicating road conditions, is followed by massive problems of trafficsafety. And this is closely related with the aerodynamic characteristic. When driving in realenvironment, for example, sudden changes of the air flow around the body is possible toalter the aerodynamic force and affect its driving stability, making the car sideslip or rollover. This mainly results from changes of transient characteristics. China covers a largeterritory, and its topography, climate and traffic condition is complex, making the suddenchanges of the airflow occur frequently.According to Japan’s Shizuoka survey, traffic accident occurs in the condition of a sharpturn was50percent. The similar conclusion is attained by Audi, its research shows thatnumbers of traffic accidents around the curve are upsurge with increasing speed. At present,numerical simulation and wind tunnel test are adapted for aerodynamics research of vehicle,and the study for driving straightly mainly includes crosswind, platoon, overtaking andpassing etc, and that for driving in the crooked roads concentrates on vehicle systemdynamics, man-machine engineering and traffic safety. However, the access to informationabout aerodynamic characteristics when going around a curve is restricted. What will happento the transient flow field around the vehicle? How will this affect the transient aerodynamiccharacteristics? Figuring out these problems will be beneficial to find out the factorsaffecting the stability of vehicle in bend condition, put forward reasonable measures, andimprove driving stability and safety. In all, the research on transient aerodynamiccharacteristics of vehicles traveling around a curve becomes very significant.The trimmer and overlapping grid of STAR-CCM+are chosen as dynamic meshingscheme to simulate the motion of vehicle in this paper, based on the characteristics of different grid strategies. In the subsequent verification of research methods, aerodynamiccharacteristics and flow field distribution obtained by transient simulation are in accordancewith the result present by steady simulation in the same condition. Therefore, the use of StarCCM+overlapping grid technology for subsequent aerodynamic characteristics and futurecomplex motion is feasible, which verify the feasibility of methods and techniques.Meanwhile provide a proper method for future study on aerodynamic characteristics ofvehicles traveling on a curve.Based on this, driving at the same speed with different bend radius and different speedbut same radius are simulated, in which process simplified SAE model restricted byHighway Design Standards are adopted. It can be found the flow field distribution isasymmetrical in terms of the longitudinal vertical plane of car body, which generatesaerodynamic force and torque. The values of Side force, rolling moment and yawingmoment, which have significant effect on vehicle driving, show a similar tendency, so as theflow distribution. With the decrease of corner radius and the increase of driving speed, thevalues of side force, rolling moment, yawing moment have increased, though not much.By simulating vehicle meeting in curve, the largest wave amplitude is lateral force androll moment among aerodynamic six-component. Its floating extremes have obvious positiveand negative asymmetry, the fluctuation of side force and rolling moment of the car in theinside corner is slightly larger than that in the outer corner. This reflects the differencebetween crossings in a crooked or linear road.It can be found by further analysis on the aerodynamic six component diagram that, inthe process of crossing(0.252s), the side force and the rolling moment of two cars, whichhave the largest fluctuation, change their direction and quickly achieve their extreme points.The peak value of side force of CAR1is about42N while the rolling moment is around30N·m. Though little from the perspective of the concrete value, the very short time and thedanger of corner make drivers hard to make a timely response, causing catastrophic effects,especially at the moment the vehicle is on the brink domain of system dynamic stability.