Research On Aerodynamic Characteristics Of The Crossing Process Between Van And Bus

With the explosive growth of car ownership and development of road traffic infrastructures,the driving environment has been more and more complex and diverse.The circumstances of crossing,overtaking and curve driving commonly occur.The complex conditions will lead to the mutual interference of the flow field around the vehicles,and affect the aerodynamic.What more serious is that when the speed is too high,it will decrease the handling stability and safety.What’s more,the vehicles are often affected by crosswind when driving on the road.The speed and angle of the crosswind will cause dramatic changes of the aerodynamic characteristics.In view of these facts,in order to ensure the driving safety,it is of great significance to research the aerodynamic characteristics of the crossing between van and bus under various conditions.This paper mainly adopts transient numerical simulation method to study three-dimensional flow field of the crossing condition between van and bus.The analysis of the flow field is aimed to research the change law of aerodynamic characteristics as well as the influence on the handling stability and safety.The research in this paper mainly includes four following aspects.First of all,conducted transient numerical simulation of single van at the speed of 30 m/s,thus figure out aerodynamic drag coefficient and flow field distribution around the van.The method was validated by comparing to wind tunnel experiment result and former related data.It laid the foundation to further study and analysis of crossing circumstance.Dynamic mesh technology was applied to realize transient numerical simulation of crossing circumstance between van and bus at four speeds of 5m/s,10m/s,20m/s,30m/s.By studying the influence of various crossing speeds,the changing law of transient aerodynamic characteristics was discovered.The aerodynamic drag coefficient and aerodynamic lift coefficient present sinusoidal variation by and large.The aerodynamic lateral coefficient fluctuates slightly as the interference of tail vertex.With the rise of crossing speed,the mutual interference of the flow field between van and bus increases as well as aerodynamic coefficients.Furthermore,the changing reasons of aerodynamic characteristics are elaborated from the aspects of surface pressure,tail vortex and velocity distribution.The impact of crosswind on van and bus when crossing was studied under three different crosswind speeds of 3m/s,6m/s,10m/s.The crosswind triggers severe changes of aerodynamic coefficients.And with the increase of crosswind,aerodynamic coefficients grow rapidly especially aerodynamic drag coefficient and aerodynamic lateral coefficient.Besides,the reasons are expounded by analyzing pressure and velocity contour on the cross section of Y=1.0m.In addition,the probable problems of safety and driving stability are also explored.Transient numerical simulations were conducted for the crossover process at the crosswind angles of β=15°,30°,45° respectively,and the variation of the aerodynamic coefficients with the crosswind angle was summarized.With the increase of the lateral wind angle,the aerodynamic lateral coefficient of the van gradually decreases,and aerodynamic drag coefficient increases continuously.But the aerodynamic drag coefficient of the bus gradually decreases.The reason for the change of aerodynamic coefficient is further explained by analyzing the distribution of pressure on the surface of van and bus at the crossing position of X/L=1.0.This paper mainly studies the influence of vehicle speed,crosswind speed and crosswind angle on the aerodynamic characteristics,and summarizes the variation of aerodynamic coefficients.The reasons for the change of flow field around the vehicles are explained from the aspect of automotive aerodynamics,which provides a reference for the driving safety under complex conditions.