Automobile Aerodynamics Research On Style Design And Optimization

The style design is an important process in vehicle design project, the key factor is aesthetics from industry design and aerodynamics from engineering.In industry design the stylists need to take into account the body shape aesthetic feeling,company brand,customer experience,etc,but the aerodynamics concern how to reduce the resistance force and the noise and the stability in high speed driving,the two side is different in thinking habit and design method, how to integrate them so the final vehicle is perfect in styling and aerodynamics is an challenging problem.Except for the forward design,optimizing the existent vehicle aerodynamics performance is another research point, current minor iterative optimizing method need to modify the local part trial and error,is an blindfold and low efficiency method;The main optimizing method in engineering field such as inherit arithmetic is appropriate for the inerratic object which is simple and can be parameterized,it is not suitable for the vehicle model which is complex and include a mass of free-form surface,so an aerodynamics optimizing method specialized for automobile is necessary.For aerodynamics research technique,except high cost wind tunnel test,CFD(Computer Fluid Dynamics) is another popular way.After thirty years development it is an almost advanced technique, currently such as turbulence model and mesh subdividsion is most concerned,because CFD is an all-around process,it is possible to improve the efficiency and precision from model aspect.So enhancing the integration between aerodynamics and industry design,improving model optimizing technique,increasing the efficiency and precision of CFD simulation,are necessary for automobile style design and aerodynamics design,and the vehicle aerodynamics performance is correlative with dynamic performance,fuel consumption and high speed stability.Good aerodynamics design is important for entire vehicle developing project.The target of this paper is to improve vehicle aerodynamics condition,made research and explore in design method and design technique.In design method aspects,two different direction was discussed:how to integrate aerodynamics and aesthetics in forward design,how to improve efficiency and quality in later stage optimization;In design technique aspects,the research focus on CFD simulation and optimization,because witout advanced CFD technique any design method cannot get good result,so the exchange between CAD model and CFD was researched.The key technology:1. The integration mechanism between aerodynamics and aesthetics in vehicle body forward designIn the process of vehicle body forward design,if a ideal model is chosen as start point which is perfect in aerodynamics performance,it is a great help for next design process.But it need to sculp and modify on the smooth ideal shape,and this work flow is not accord with traditional habit, so it is necessary to constitute a integration mechanism between aerodynamics and aesthetics.The correlative key technique is:1) Build up the describing mechanism for style gene.Research the describing mode and definition standard for aerodynamics gene and style gene,establish corresponding describing measure and mathematics model based on bodywork design platform,this model can fulfil the request on exchange and evolution for model describing in CAD platform.2) Establish integration mechanism in design process.Research how to integrate and syncretize for aerodynamics gene and style gene,include2D integrating and3D integrating.2. Optimizing holistic aerodynamics layout for finished vehicleFor reducing cost in redesign, the automobile company need to modify the vehicle limited to improve aerodynamics performance; the style project deigned by stylists also need to be optimized.Traditional minor iterative optimizing method need to modify the local part trial and error,is an blindfold and low efficiency method.So a new kind of optimizing method aimed to finished vehicle is necessary.The correlative key technique is:1) Filtration for non-aerodynamics parts.The actual vehicle include a great deal of non-aerodynamics parts which have limited influence to holistic flow field,but it greatly decrease the efficiency in CFD simulation and optimizing and it is difficult to find out the disfigurement in aerodynamics layout.So it is feasible to filtrate these parts and optimize the basic shape.2) Distortion technique.It is a modify technique based on control box,it suits the freeform surface in vehicle bodywork and can freely modify the shape,avoids the limitation in minor iterative optimizing method.3. Improve the efficiency and quality in CFD simulation and optimizingCFD simulation is a verv important measure in automobile stvle design,from the viewpoint of CAD model and calculating mesh,a new kind of model technology fit for bodywork surface is brought out,it can greatly improve the efficiency in model optimizing and maintenance good precision in CFD simulation.The correlative key technique is:1) Subdivision mesh technology.In vehice deign progress the traditional nurbs surface have the advantage of high precision and good smoothness,but the model hiberarchy is complicated because the surface is made up of patches,it has the disadvantage of low efficiency and freeness in mesh subdiving process,by introducing new subdivision mesh model instead of nurbs model,the efficiency and quality in CFD simulation can be improved and the precision can keep in acceptable level.2) The features for calculating mesh.In mesh generating process,in order to improve simulation precision it is feasible to make feature work on mesh object so the calculating mesh is more close to original model and the nodes can snap to geometry information on bodywork.