Research On High-Speed Aerodynamic Stability Of A Vehicle In Crosswind Condition By Transient Coupling Method

With the rapid development of domestic automotive industry,soaring construction of the highways,and continuous increasement of vehicle average running speed,consumers for vehicle high-speed safety quality put forward the ever-increasing demands,so it is imperative to the research the high-speed driving safety of a vehicle.Meanwhile,due to china has a vast territory,the topographic features are very difference in china,as a result of the nature wind environment of many places may be very poor,and the natural crosswind directly affect aerodynamic stability of a vehicle at a high speed,then it causes aerodynamic stability of vehicle to decrease,and even result in side slipping,yawing and rolling over,etc.instability phenomenon,in extreme cases,triggering serious safety problems.However,the traditional methods can not truly reflect the coupling effects of flow field and vehicle system for the study of the high-speed aerodynamic stability of a vehicle in crosswind condition,so the study on the transient coupling method to the problem for improving vehicle high-speed driving safety has important theoretical guiding significance and engineering application value.By attaching importance to numerical simulation method,combining with wind tunnel experiments,an asynchronous transient coupling simulation method for high speed aerodynamic stability of a vehicle in crosswind condition has been proposed from the viewpoints of aerodynamics and system dynamics coupling.And based on this research,this paper mainly researches the automobile aerodynamic characteristics and stability under strong crosswind.The main research content is as follows:1.Based on system dynamics and foundation models,the vehicle multi-dof dynamics and the virtual prototype model were establilshed,and through the front wheel step input and steady lateral force input virtual experiment contrast analysis,illustrated the reliability of the multi-dof vehicle dynamics model.2.By the analysis of the wind spectrum of natural wind measured data,the random fluctuating wind model of the size and direction are variation with time.Meanwhile the related research and wind tunnel esperiment of crosswind numerical simulation method and turbulence model adaptability has carried.Established the communication mode of coupling analysis,built the one-way coupling and two-way coupling simulation method by combined with fluid and system dynamics simulation software,and illustrated the necessity of two-way coupling method to the problem of vehicle stability in crosswind condition through comparative analysis of one-way coupling and two-way coupling simulation method about this problem.3.Focused on the limits of the steady coupling methods for high-speed aerodynamic stability of a vehicle in crosswind condition,and combine dynamic mesh technology,an asynchronous transient coupling simulation method has been proposed,which improved iterative mutations phenomenon in the two-way coupling method,made up for the deficiency of the steady coupling method,and analysed the difference about the two methods for high speed aerodynamic stability of vehicle by comparison with that the steady coupling simulation method.4.The change rule of influence for different external factors of the two crosswind model of gust and local winds to the high-speed aerodynamic stability of a vehicle in crosswind condition were studied by using this asynchronous transient coupling simulation method.Meanwhile,this paper proposed a weighted of two factors evaluation index of the stability of vehicle in crosswind condition based on risk function and weight distribution,and analyzed the safety driving speed of specific crosswind environment.Finally a new improvement design scheme of vehicle side skirts was proposed,the comparison show that the improved complex side skirts in the high-speed aerodynamic stability of a vehicle in crosswind condition than normal side skirts were obviously improved.