Simulation Research On Aerodynamic Characteristics And Driving Stability Of Truck Within Unsteady Wind

As rapid development of automobile industry and expressway construction comes with economic development,the application of commercial truck is becoming wider and wider as well as the driving environment is increasingly complex.Especially to the van,the comprehensive function of various factors lead to crosswind environment becoming one of the great threats of stability and safety,such as: the hostile and complex roads,the influence of varying weather conditions,the high shape sensitivity of truck,the sensitivity increase caused by higher speed.All kinds of elements lead environment crosswind to be one of the threats of vehicle stability and safety.Under the influence of unsteady wind,aerodynamic six components acting on the van will come to a fast,strong random variation trend,thus the flow field surrounding truck appears complex features.The influences of aerodynamic lateral force,rolling moment and yawing moment of the veichle are most apparent.The above influences mainly appear to two aspects: one is the influence on vehicle lateral properties,which weaken the ability of straight driving of vehicle,is caused by lateral force and yawing moment of the crosswind,thus the vehicle come to a lateral deviation.When drivers get exhausted by operating frequently,it is easy to cause the vehicle deviate from the original line and come to an accident.The other influence is rolling safety of vehicle.When the aerodynamic force value is too large,direction changes,or its rate is too large,vehicle under high speed condition will appear a trend of rolling and the possibility of rollover has greatly increased.In this study area,previous researchers only focus on research of aerodynamic characteristics,or only on stable wind environment,and less research on the improvement of the vehicle driving stability.Therefore the study of influence caused by unsteady wind on aerodynamic characteristics,the flow field structure and driving stability of van has great significance on enhancing driving safety,operating stability,and riding comfort of van.In this paper,the research content mainly divided into three parts.The first part mainly focuses on the determination of the numerical simulation method and verifies method feasibility.According to the analysis,the results got in this paper by transient simulation method have a good consistency with steady simulation results and wind tunnel results.The second part uses the chimera grids method for the transient simulation of moving vehicle.The simulation conditions mainly includes linearly varying crosswind condition,accelerating condition under constant crosswind and sinely varying crosswind condition.The simulation variables under linearly varying crosswind are two different viehcle speeds and three different crosswind change rates.According to the analysis,it is obvious that aerodynamic lateral force,rolling moment increases with the increase of wind speed,yawing moment,pitching moment fluctuate in the trend of rise,aerodynamic drag increases at first and decreaseses later.In the accelerating condition there are three various conditions about three different speeds come to same speed are simulated under the constant crosswind,in the process of simulation the aerodynamic drag and side force increase,but their coefficients decrease with the decreasing side-slip angle.Lateral force and yawing moment appear larger fluctuation in the beginning of accelerating stage.Each kind of the final value of aerodynamic force is related to the time which is needed to reach the same speed of cross wind and vehicle motion.Sinely varying crosswind lead the aerodynamic force to a similar change in sine form and its variety range later is different from the beginning.This paper mainly analyzes flow field structure changes from the aspects of pressure,velocity and vorticity.In the third part complex vehicle system dynamic model is established and system dynamic simulation is carried on to reach the simulation of driving stability under unsteady wind simulation.Qualitative and quantitative evaluation index is used to analyze the trend of lateral deviation and rolling motion.It turns out that in high crosswind rate and high vehicle speed condition under linearly varying crosswind came to a dangerous situation of deviation from original road and great trend of rolling motion.Sinely varying crosswind lead vehicle lateral migration direction change immediately and alternative of vertical load relation of tires on different side.Finally through the analysis of the effect on driving stability of the suspension stiffness design,the exploration to improve the structure parameters of the driving stability under crosswind is carried on.