Analysis Of Automotive Aerodynamic Characteristics And Research Of Drag Reduction Based On FLUENT

Whether it is for the traditional fuel vehicles or modern electric vehicles,Energy Saving and Environmental Protection are the eternal themes of the car design.Nowadays,many countries in the world are facing the severe oil crisis,and the key technology of automobile battery can not be broken through,so oil as a kind of nonrenewable resource can not be replaced by electricity completely,and this is the reason why it is important to design vehicles of low aerodynamic drag.With the development of China’s automobile industry and the rise of independent brand vehicle,the speed of cars have greatly improved.Studies have shown that when a car was driven faster,its aerodynamic drag grows bigger,and the amounts of fuel consumption will rise,well-shaped vehicles have lower aerodynamic drag and better fuel efficiency of automobiles.In this paper,3D surface model of car was established in CATIA according to a compact SUV,and this geometry model was mesh into unstructured tetrahedral in ICEM,the grids file was imported to FLUENT for simulation,the Realizable k-ε turbulence model and Standard Wall Functions were selected to improve the accuracy of the simulation,finally,calculation results were imported into TECPLOT for post processing.First of all,this paper introduces the general simulation process of automobile external flow field in absence of crosswind,and calculated the coefficient of aerodynamic drag and coefficient of aerodynamic lift.Then five kinds of operating conditions in crosswind of five different yaw angles β-6deg,12 deg,18deg,24 deg and30deg-were simulated,and the simulation results show that aerodynamic characteristics of vehicle under crosswind is quite different from that of it with no crosswind.As the increase of the yaw angle of crosswind,three aerodynamic coefficients of the vehicle increased in different degrees,and the aerodynamic coefficient of lateral force rises mostly.Through the digital modeling technology of the CATIA,five key structure parameters-tilt angle of front window,tilt angle of rear window,front upswept angle,ground clearance and rear upswept angle,which influence the appearance of cars mostly-were selected.Orthogonal tests of 16 models of five factors and four levels were carried out.Through test results the optimal level of each factor were got,the top two factors that influence the aerodynamic coefficient of drag of vehicle most are tilt angle of rear window and ground clearance.The optimization model was got by combining the optimal levels of each factor together.Then the other four factors of the optimal model are fixed,and the influence of four different levels of one of five factors on the aerodynamic drag is studied.Finally take the optimization model for simulation,it found that the coefficient of drag of this model declined to 0.3506,6.98% lower than the original model of vehicle.Through analyzing the velocity distribution,pressure distribution and turbulent kinetic energy distribution of the optimization model and the original one,it is found that the aerodynamic characteristics of the optimization model improved,this is the reason why the coefficient of drag of optimization model declined.Based on the orthogonal optimization model,second optimization of this model was taken,tilt angle of front face of engine cover was changed from 0deg to 8deg,the radius of engine cover was increased from 200 mm to 300 mm,the simulation results show that the second optimization model of resistance coefficient decreased to0.3425,2.3% lower than that of the orthogonal optimization model.This paper attained good results of optimization.