Simulation And Wind Tunnel Verification Of An SUV Aerodynamic Characteristics

SUV,as a preferred model of urban emerging car buyers,has become the main choice of the automobile market in recent years.Optimizing the aerodynamic characteristics of the vehicle has become the research focus of automobile companies,research institutes and universities.Guided by computational fluid dynamics(CFD)simulation and wind tunnel test results,adding appropriate aerodynamic accessories is one of the main ways to improve the external flow field and aerodynamic characteristics of the vehicle.Taking an SUV as the research object,this paper designed 6 kinds of drag reduction aerodynamic accessories,and carried out numerical simulation calculation as well as wind tunnel test on them.Based on the lowest wind resistance of the vehicle,this paper also designed shark fin attachment by using bionic principle to improve the lift characteristics more.Reasonably cleaned the geometric model of the SUV,and selected the appropriate volume mesh strategy to ensure the simulation accuracy and efficiency.According to the real vehicle wind tunnel test,the simulation boundary conditions and solver parameters were determined.At the same time,the simulation residual value and wind resistance coefficient fluctuation assignment were monitored to ensure the convergence of the results.Considering the simulation accuracy,the simulation results of Realizable k-ε and SST k-ω turbulence models were compared,and the relative errors were 1.5% and 2.6%,respectively.Therefore,this paper used Realizable k-ε turbulence model to complete the simulation calculation of the basic model,and analyzed the resistance contribution area and its formation mechanism of the SUV.Based on the flow field simulation results of the basic model of the SUV,six aerodynamic drag reduction accessories were designed,including front bumper baffle,front wheel baffle ramp,rear sub-frame deflector,middle deflector of the chassis,silencer deflector and the tail,and all of them were verified in the wind tunnel.The results show that aerodynamic accessories contribute to the drag reduction of the vehicle to varying degrees.The drag coefficient of the vehicle combined with 6 aerodynamic accessories was reduced by 6.25%,which effectively achieved energy saving and drag reduction.Guided by the bionic principle and taking the optimal drag reduction scheme as the basic model,a shark fin accessory was designed.When the shark fin accessory was installed on the front and middle of the SUV chassis,the lift of the vehicle can be reduced,while the lift of the vehicle was slightly increased when the accessory was installed in the rear of the SUV chassis.The height of the shark fin accessory was used as the design variable to optimize the lift of the vehicle,and the sample points were designed by the Optimal Latin hypercube design.The Kriging approximate model of the vehicle lift was built based on the design variables,and the global optimization was carried out based on the multi-island genetic algorithm.The optimization results show that when the height of the shark fin attached device in the front,middle and rear of the chassis is 6.9mm,26.1mm and 16.7mm,respectively,the lift force of the vehicle decreases by 5.7%,and the drag coefficient of the vehicle decreases by 2counts.Therefore,the lift performance of the vehicle is improved on the basis of the optimal wind resistance coefficient.