Study Of Aerodynamic Interference Characteristics During Multi-vehicle Overtaking Process

With the rapid development of our national highway and theadvancement of vehicle speed, the time of high speed driving is becomingmore and more. People put forward higher and higher requirements to thehandling stability, safety and comfort of a road vehicle. And the handlingstability, safety and comfort of a high-speed vehicle are determined to agreat extent by the flow characteristics around the vehicle. When vehicle isrunning with high speed, the flow and pressure field varies continuously.During multi-vehicle running, the turbulent characteristics and aerodynamicphenomena are especially complex. Such a phenomenon is identified asaerodynamic interference between vehicles. The interference betweenvehicles will influence the aerodynamic characteristics of vehicles severelyand have a great influence on the handling stability of a road vehicle.With the development of national economic and advancement ofvehicle quantity, the running conditions are becoming more and morecomplex. And different dimension and speed vehicles often overtake.When high-speed vehicles, especially light vehicle (such as passenger carand motorcycle), is overtaking or overtaken by heavy vehicle, vehicles willbe subject to drift because of strong aerodynamic interference, This willcause loss of driver steering or control and arose traffic accident. The trafficaccidents related to overtaking is a part of collision accidents on highwayevery year, which brings severe loss to the life and properties of nation andpeople. Due to the lack of research on multi-vehicle aerodynamicinterference characteristics, it's hard to control the abrupt traffic accidentsduring multi-vehicle overtaking. Therefore, this research has an importantrealistic significance. In this paper, a commercial CFD (Computational Fluid Dynamics)solver Star-CD is used to study the aerodynamic interference actionmechanism during multi-vehicle overtaking process. It can perfect furtherthe automobile dynamic model, simulate the vehicle's motion more really,develop more real driver-vehicle-circumstance simulation system andprovide theoretical foundation for vehicle intelligent control. And revise theresearch conclusion with only a single vehicle considered. The researchconclusion can be applied to traffic safety system control and has animportant significance for controlling traffic flow and speed, reducing trafficaccidents and ensuring traffic safety. This paper firstly presents theory basic of automotive flow field andanalyzes the characteristics of automotive flow field. Several arithmetic arepresented, such as finite difference method, finite element method andfinite volume method. And fluid dynamics control equation, turbulent modeland grid discretization etc. are simply introduced. Then the single vehicle external flow field is simulated. This is thebase of researching aerodynamic interference during multi-vehicleovertaking process in order to contrast the external flow fields under twoconditions. Since other staff in this task team has simulated the MIRAmodel in multi-vehicle research, a certain homemade bus is studied withnumerical simulation. The numerical simulation results are compared withcorresponding wind tunnel test results. And the validity and accuracy of theCFD solver is verified, which provide the numerical simulation for vehiclesovertaking process with the calculation basis and guarantee. Throughanalyzing the distribution of velocity and pressure of flow field around bus,the paper discusses the flow mechanism of flow field around bus. Yamamoto et al. report that when the difference between the velocityof the passing automobile and the passed automobile is relatively small(5.6m/s or less), static aerodynamic characteristics can explain the passingphenomenon. Thus, concerning the static simulation method, theovertaking process is treated in incremental steps. The continuousunsteady overtaking process of two vehicles, traveling with constant butunequal speeds is replaced by a finite number of steps; in each the relativeposition of both vehicles changes. Five typical longitudinal relativepositions and two vehicles with the speed of 30m/s are selected to simulatethe overtaking process and study the aerodynamic interferencecharacteristics. Five conditions under five longitudinal relative positionsand three lateral distances are simulated. The numerical simulation resultsagree with the wind tunnel test results, which verifies the validity ofnumerical simulation procedure and results. After data processing andanalysis, it's concluded that during overtaking process the aerodynamicforce varies with the longitudinal relative position. When the front end ofovertaking vehicle reaches the rear of overtaken vehicle, the side forcecoefficient and drag coefficient reach the maximum. When the front end ofovertaking vehicle reaches the middle of overtaken vehicle, the side forcecoefficient and drag coefficient reach the maximum. On the base of formerresearch, study the affect of yawing moment, side force, rolling moment,driving speed and relative speed on vehicle handling stability and safety,and put forward that a safety lateral spacing should be ensured duringovertaking process. Through simulation for the aerodynamic characteristics of multi-vehicle...