Research On Aerodynamic Characteristics Of Two-Lane Change Overtaking Based On CFD

With the large-scale coverage of highways and the rapid development of the automobile industry,the safety of automobile driving on the road has attracted much attention.When vehicles are driving at high speeds on the highway,the phenomenon of two-lane overtaking when there are vehicles in both lanes is becoming more and more frequent.When driving in this state,the safety and stability of the car have attracted much attention.At the same time,the vehicle shape also directly affects the flow field around the vehicle,and the external flow field of the car directly affects the driving stability,economy and safety.Therefore,according to the changes in the outflow field of the vehicle and the change of the flow field of the two-lane overtaking process,it is a very effective method to take corresponding measures to improve the stability,safety and economy of the car.In this paper,the CFD(Computational Fluid Dynamics)software performs transient simulation of the two-lane overtaking process,studies the outflow field change of the vehicle during the two-lane overtaking process,and analyzes the reasons for the change of aerodynamic force during the two-lane overtaking process.Before analyzing the overtaking process,the selected SUV model is first optimized for local shape,and a series of pre-processing work such as geometric cleaning,meshing,and setting boundary conditions are performed on the model,and the drag coefficient is finally determined to be Cd=0.353 after calculation.Through the analysis of the obtained body surface pressure cloud map,airflow velocity vector diagram and vortex map,a local improvement scheme is formulated,and the most ideal wind resistance coefficient is finally obtained through the local improvement of the body.Streamline the processing of the optimized car model and perform transient simulations of the two-lane overtaking process.The GAMBIT software creates a two-dimensional two-lane overtaking model,sets the model mesh size and the boundary conditions of the calculation domain.The mesh model is imported into FLUNENT,and the Profile program is written to realize the movement process of overtaking,and the pressure cloud map,speed vector diagram,streamline diagram and vortex diagram of the two-lane overtaking process are calculated and analyzed,and finally reasonable suggestions for two-lane overtaking are given.Studies have shown that in the process of two-lane overtaking,there are strong pressure and air flow rate changes around the three vehicles,when overtaking vehicle is between two overtaken vehicles,the flow field changes more complex,with the change of the relative position of the vehicle,the vortex form around the three vehicles changes significantly,the vortex changes consume the energy in the flow field,so that the body of vehicle force changes;during the driving process,the lateral force,the wind pressure center position and the pendulum moment of the three vehicles have changed significantly.On the basis of the two-lane overtaking process,the numerical simulation of the overtaking process is carried out on different speeds and models,and the study shows that:with the increase of speed,the pressure difference between the overtaking vehicle and the overtaken vehicle at the maximum lateral force increases significantly,and the maximum lateral force of the overtaking vehicle and the overtaken vehicle increases approximately linearly;when overtaking is carried out in the case of large vehicles in both lanes,in the case of the same speed,the maximum lateral force of the overtaking vehicle is significantly greater than that of the same model.When overtaking the large vehicle,the driving stability of the overtaking vehicle will be more affected.