Aerodynamic Shape Optimization Design Of A Sedan Modal

At present,The car ownership continue increasing, the mount of automobile production and sales exceeds 13 million in the 2009 in China market. And the automobile ownership reaches 137 million in the 2013, increases to 154 million in the 2015, China became the world’s the largest producer and consumer. As the development of the highway and increase of automobile speed, which result in energy consumption and environmental pollution problems. In addition to the development the new energy automobile, reduce air drag also is the important way to solve the energy problem. When traveling, most gasoline will be consumed by overcoming the air drag, so the main idea of thesis is to reduce the air drag by optimizing the automobile shape, and reduce the gasoline consumption, which is benefit for the energy-saving and emission-reduction of auto industry.In the car body design, the first step is the CAS engineer builds up the model for the CFD analysis, which is close. The next step the CFD engineer evaluate the aerodynamic characteristic by calculating, and give some suggestions, later the CAS engineer will redesign the new model according to the experiences and suggestions, the CFD engineer will analysis again, which is multi-iterations process. Until the design be able meet requirement or the time is not enough. In the analysis process, CFD engineer need to simplify the model,mesh,set boundary condition,extract the result, report, most of the man power and material resources will be used in the repetitive work. With the development of the computer capability, the improvement of the CFD software, mesh morph, DOE, approximation model, parallel technology, the auto optimization is an inevitable trend by combining the mesh morph software, CFD software and optimization software. On the base of these technologies, setting up the auto optimization platform about automobile shape, which including the CAD, CFD, mesh morph, DOE, approximation optimization technology, the purpose of thesis is to find the optimal assembly of car parameters, and research the aerodynamic characteristic for each parameter, finally, which be able to instruct the car body design.In the thesis, consider the Mira model, analysis the external flow-field of car body in Starccm+, the objectives is: 1, by evaluating the external flow-field of car body, find the important parameters for air drag, and remove the not important parameters 2. RecodeMarcos command about mesh, boundary condition and extract result, which be used in the next step. 3, find a suitable mesh method and parameter configuration, which be used in the next analysis.In the thesis, by analyzing the external flow-field of car body, get four parameters which is most influential for air drag, is angle of engine cover, area of car front, angle of rear cover, area of car tail. Build up the DOE matrix which has 20 levels, establishing approximation model by DOE result, and check the accuracy of approximation model by calculating. By optimization, the air drag reduces to 12.8% than before; the result is good and has no influence to the car style. Finally, evaluate the each parameter; further understand the relationship between four parameters and each parameter.In the thesis, the main purpose is to build up the auto optimization platform, and to design car body fast and to save the manpower and the material resources. Further understand each parameters is influential for the air drag, which is benefit for instruct the car body design. The auto optimization also can be used in vehicle development.