Optimization Of Partial Body Shape To Reduce Sedan Aerodynamic Drag

The rapid development of automobile industry has brought huge economic benefits to the country,but also brought some problems,such as energy consumption and environmental pollution and so on.Faced with dwindling non-renewable resources and worsening smog,reducing vehicle fuel consumption and exhaust gas emission is an urgent problem that every automobile enterprise should be solved.A large part of the energy consumption in the course of driving is to overcome the driving resistance.And with the increase of vehicle speed aerodynamic drag becomes the main resistance that the vehicle need to be overcome.So optimizing the aerodynamic shape of the sedan and then reducing the driving resistance can effectively reduce vehicle fuel consumption.This paper selects the sedan as the object of the research and studies how to optimize the aerodynamic drag reduction of the partial of sedan in the later phase of styling design.The overall shape of sedan is basically determined in the initial phase of design.In the later phase of styling design,limited by general arrangement,structure and other properties,we cannot make a big change in styling.On the basis of not affecting the overall shape,the optimization of aerodynamic characteristics of partial sedan is to study the key parts which effect the aerodynamic drag to achieve the effect of drag reduction.First of all,this paper has carried wind tunnel test and numerical simulation to the basic model of sedan,the scale of which is 1:2.And selected the credible simulation strategy through the comparison between the experiment and the simulation,and the basic model is improved to make it closer to the real sedan.According to the different optimization method,vehicle optimization is divided into two parts: optimization of the upper body,interior and underbody optimization.The upper surface of the sedan mainly changes through the method of refined deformation.The interior and underbody is mainly achieved by adding diversion components and re-optimization of the components.According to the varying degrees of complexity of the components,the method of drag reduction is divided into single variable optimization and multivariable optimization.The single variable mainly targets the parts which have relatively simple geometry,it studies how to effect the results with the changing of variable by changing the single variable.The multivariable mainly targets the parts which have relatively complex shape,and the use of more control variables can better change each local feature.In this paper,based on Hyperstudy,a set of optimization flow is established for the multivariable research by using morph software and fluid simulation software.The whole process includes design of experiment,fitting model and optimization solution.While improving the efficiency of optimization,we can analyze the data in order to solve the optimal combination of variables.According to the analysis of the flow field of the Base model,the optimization part of the upper body contains the front fender,A pillar,rear fender and rear trunk lid.According to the continuity of the curved surface of the body,choose different morph methods to modify the partial shape and keep the surface smooth and continuous as well as not to cause a great impact on the shape.Each part is controlled by 1 to 4 variables,and the experimental design is carried out by using Hammersley Sequence Sampling method.Selecting the appropriate fitting model by comparing and solving the corresponding variable parameter of the minimum drag coefficient with the help of optimization algorithm.The optimization results are analyzed in details.Eventually,according to the calculation,the front fender reduced resistance by 1.23%,A column reduced resistance by 3.09%,the rear fender reduced resistance by 1.85% and rear trunk lid reduced resistance by 7.12%.The interior and underbody are not obvious for the surface of the sedan.Therefore,the partial optimization for this position is mainly based on the analysis to determine the optimal position,reduce the resistance by adding spoilers,and by means of the optimization process,optimizing the spoilers to make it better to reduce the drag.The interior of the body reduced resistance by 2.01% by optimizing the grid deflector,the front wheel house reduced resistance by 2.35% after optimization,and the chassis tail deflector reduced resistance by 6.47%.Finally,combining the schemes.The optimizing function should not be overlapped when combining the prioritization schemes.The final prioritization schemes includes the front fender,A pillar,the rear fender,rear trunk lid,grille deflector,and chassis rear deflector.The six schemes are combined to achieve a final effect of drag reduction of 14.55%.