Joint Study On Aerodynamics And Handling Stability Of FSAE Racing Car Under Unsteady Wind

With the rapid development of FSAE race(Formula SAE),i.e.Formula Student Automobile Competition,the driving speed of racing cars has increased year by year,and the aerodynamics of racing cars as the main research content has been widely concerned by the teams within foreign countries.For the racing car,the aerodynamic force on the pneumatic device finally acts on the tires through the transmission of the body and suspension.The effect of aerodynamics on the handling stability can be seen to be significant.Considering the large amount of basic data and computational resources required for joint simulation,few schools at home and abroad consider the interaction between aerodynamic characteristics and handling stability in the simulation design stage,but this interaction occurs in racing cars all the time,so the joint study of racing car aerodynamics and system dynamics becomes especially important.In this paper,the FSAE racing car of Jilin University participating in domestic races in2019 is used as the research object,and the STAR-CCM+ and Car Sim software are used to combine the wind tunnel test of the racing car,the numerical simulation of aerodynamics of the simplified model of the racing car,and the simulation of the dynamics of the racing system to establish the closed-loop design process of the aerodynamics of the FSAE racing car,and to conduct the joint study of the aerodynamic characteristics of the racing car under unsteady wind and the handling The joint study of aerodynamic characteristics and handling stability under unsteady wind is carried out,and the aerodynamic parameters of FSAE racing car are optimized.The main contents of the article can be divided into the following parts:First,based on the wind tunnel test data of FSAE racing car,the simulation strategy of the external flow field of the whole car is improved by filtering the turbulence model and optimizing the boundary layer mesh,and the error between the simulation and test values of the improved simulation strategy is about 6%,which lays the foundation for the simulation of the external flow field of the racing car under different working conditions later;Secondly,based on the actual working conditions of FSAE racing cars,simulations are carried out for two types of working conditions with and without the effect of side wind,by studying the aerodynamic characteristics of racing cars under different working conditions,analyzing the reasons for the differences in aerodynamic characteristics of each working condition,exploring the influence of each aerodynamic device on the aerodynamic characteristics of the whole vehicle,and obtaining the aerodynamic parameters of racing cars under each working condition to provide data support for dynamics simulation;Thirdly,based on the aerodynamic simulation data and racing car assembly characteristic parameters,a joint simulation model of racing car aerodynamics and whole vehicle dynamics was built by Car Sim,and steady-state slew simulation and snake test simulation were carried out for the racing car according to the event dynamic project,and the simulation data were evaluated by combining with the national standard QC/T 480-1999.Considering the influence of unsteady wind effect,the snake test simulation was carried out to compare the analysis of racing car stability with and without side wind effect,and the analysis of the influence of side wind speed size,side wind effect time,discontinuous side wind and side wind direction change on racing car handling stability,through the joint simulation study of racing car aerodynamics and racing car system dynamics,the influence of unsteady wind effect on FSAE racing car handling stability was realized comprehensive prediction of the effect of unsteady wind action on the handling stability of FSAE racing cars;Fourthly,we summarize and analyze the problem of large fluctuations of the aerodynamic parameters of the car when the body attitude changes in the joint simulation of aerodynamics and system dynamics,and optimize the design of the aerodynamic parameters of the FSAE car in the pitching condition,and verify the optimized scheme through the eight-word surround simulation,steady-state slewing simulation and snaking test simulation.Analyze the relationship between the wind pressure center reference point and the aerodynamic force distribution,and the aerodynamic force is distributed to the front and rear axles of the car to obtain the ratio of aerodynamic force distribution between the front and rear axles of the car after the optimization of aerodynamic parameters,which provides guidance suggestions for the aerodynamic design of the car afterwards.To sum up,this paper combines wind tunnel test,aerodynamic simulation of simplified model and dynamics simulation of racing system to conduct a joint simulation study on the aerodynamic characteristics and handling stability of racing car under unsteady wind,analyze the influence of the aerodynamic characteristics of racing car on the handling stability of the whole car,and optimize the aerodynamic parameters of FSAE racing car with the purpose of closed-loop design.The results show that after the optimization of the aerodynamic parameters,the critical speed of the car through the cornering is increased,the handling of the car is improved,the test time of the figure-of-eight surround is reduced by 0.525 s,the aerodynamic drag of the car under 15m/s wind speed is reduced by 2.91%,the downforce is increased by10.48%,the pitch moment is reduced by 82.34%,the lift-to-drag ratio is increased by 14.70%,the negative lift distribution between the front and rear axles is changed from 36.8:63.2 to The front and rear axle negative lift distribution changed from 36.8:63.2 to 43.7:56.3.The lifting and drag characteristics and aerodynamic efficiency of the car were improved significantly,and the aerodynamic performance and overall performance of the car were greatly improved.