1 Purpose and significance (including analysis ofresearch status at home and abroad)

1.1 ResearchBackground

The automobile industryis an important pillar industry of China's national economy and plays animportant role in the development of the national economy and society. Withthe sustained and rapid development of our economy and the acceleration ofthe urbanization process and the comprehensive implementation of the povertyalleviation plan, the demand for automobiles will remain at a relatively highlevel for a longer period of time, and the resulting energy shortage willbecome more prominent. In 2014, five ministriesand commissions, including the Ministry of Industry and InformationTechnology of the People's Republic of China, jointly issued the third phaseof the implementation of fuel limit standards for passenger cars. Accordingto this standard, the average fuel consumption of domestically producedpassenger cars will reach 6.9L / 100km by 2015. Vehicle fuel consumption hasdropped below 5.9L / 100km. In 2016, the Ministry of Industry and InformationTechnology pointed out on the "Energy Conservation and New EnergyVehicle Industry Development Plan (2012-2020)" that China will fullyachieve passenger fuel consumption of less than 5 liters per 100 kilometersin 2020, and the fuel consumption of energy-saving passenger vehicles willfall to 4.5 L / 100km; the fuel consumption of new commercial vehicles isclose to the international advanced level target. In 2019, the Ministry ofIndustry and Information Technology formulated the latest two nationalstandards, "Passenger Car Fuel Consumption Limits" and"Passenger Car Fuel Consumption Evaluation Methods and Indicators,"and publicly solicited opinions. It is estimated that by 2025, the averagefuel consumption of new passenger cars should be Reduced to about 4L / 100km.Judging from national policies in recent years, the state has paid moreattention to the issue of energy shortages in automobiles and has stricterfuel consumption standards for passenger cars. Therefore, the improvement ofthe automobile energy use economy and the reduction of automobile fuelconsumption have become the subjects of great concern in the modernautomobile industry.

Relevant research showsthat the wind resistance coefficient is an important indicator for measuringthe aerodynamics of automobiles. The smaller the wind resistance coefficient,the better the aerodynamic characteristics of the automobile. For every 1% decreasein wind resistance coefficient, the fuel consumption of the vehicle is savedby 0.03L / 100km. For every 5% reduction, NEDC fuel consumption is reduced byabout 1% ^[1]. Therefore, the wind resistance can be reduced byoptimizing the design of the car body and other aspects, so as to reduce thefuel consumption of the entire vehicle. The airresistance encountered by the car during driving is composed of multipleparts, of which the shape resistance accounts for about 60% of theaerodynamic resistance. Therefore, researching the aerodynamics of a car fromthe perspective of car shape is of great significance to reduce windresistance and vehicle fuel consumption.

1.2 Researchpurpose and significance

As an important part of acar, the styling design of the car body has always been a major problem incar design and development. At the same time, the fuel economy, power, andhandling stability of the car have been largely affected by aerodynamics. Howto design a car body with good aerodynamic characteristics, reduce airresistance, and make the car more economical and dynamic is particularlyimportant.

Objective of the research are: designing a light carbody shape that meets aerodynamic requirements; locally optimizing the designof each body part; establishing a three-dimensional model and simulationmodel of the car body; simulating and analyzing the external flow field ofthe car body to achieve a good aerodynamic characteristic.

Significance of the research is to fully link thecourses "Automotive Aerodynamics", "AutomobileStructure", "Automotive Theory", and "Auto Design"studied during the undergraduate period. ; In the process of research anddesign, I have a deeper understanding of the structural characteristics oflight cars and the aerodynamic design of car bodies; used virtual simulationtechnology to participate in the design of car body shapes, reflecting thefunction of computer-aided industrial engineering design; The currentadvantages and disadvantages of the body design of light-duty cars and theirprocesses; improving the design level of their own car body models; it hascertain reference significance for the future car body model design.

1.3ResearchStatus at Home and Abroad

Since the late 1950s, foreign companies began tocreate some car automobile wind tunnel laboratory for testing real carmodels. From the 1970s to the 1980s, the British A.J. Scibor Rystki and theGerman W.H. Hucho did a lot of research and practical work on the aerodynamicdesign of passenger cars. In 1976, Italian professor A. Morelli proposedaerodynamic design method based on ideal body, through predefinedlow-impedance body for post-modification limited as a starting point to formboth practical and functional aerodynamic body styling. In the 21st century,large foreign auto company starts its extensive use of CFD in conjunctionwith wind tunnel experiments to model design work, research focused on theuse of CFD technology and aerodynamic design of specific models. In 2000, GM's Rnjneesh Singh on the body CFDautomatic optimization techniques are studied, he meshing solver package andcalculate the data interface integrated package, and then a mid-size sedanhas been modified automatic and automatic simulation. 2006DaimlerChrysler Xijia Zhu et al uses a modification grid to optimize theshape of the vehicle body, by deforming the mesh across the fieldcorresponding to the outflow volume mesh indirectly deformed. In 2007,Santosh Kini et al of ESI Company studied a Cartesian automatic meshingmethod for low-quality CAD models, which can reduce the requirements formodel pre-processing. In 2008, Sandeep Dinkar Sovani and others of ANSYSresearched a fast meshing technique, which mainly aimed at the situation thatthe computational mesh generation of the real car model was tootime-consuming due to its complex appearance. ^[2]

For a long time, China has mainly produced low-speedtrucks. Considering aerodynamic factors in car styling, the automotiveindustry has started its research on aerodynamic modeling late. Since the1980s, China has begun to study the external flow field of automobiles. Inthe late 1980s, Hunan University took the lead in carrying out research on thenumerical simulation of vehicle aerodynamics, implemented 2D and 3D numericalsimulations on the outflow aerodynamic field of vehicles, and obtainedpressure and velocity distribution cloud maps of outflow aerodynamic fieldsof vehicles. In 1997, Gu Zhengqi and Jiang Lehua of HunanUniversity introduced the application of aerodynamics to the analysis ofautomobile aerodynamic performance, and pointed out its limitations anddevelopment directions, which provided important theoretical guidance for thefuture investigation of automobile aerodynamic characteristics. In 2000,after the introduction of Fluent simulation software by the FAW TechnologyCenter in China, the CFD method was applied to the research and developmentof passenger car bodies for the first time. In 2003, teachers such as JilinUniversity Fu Limin, Hu Xingjun, Tongji University Yan Peng, Wu Guangqiangand others used a variety of difference methods and turbulence models tosimulate the outflow aerodynamic field of a car, and summarized thedifference methods and turbulence models. In 2006, Zhejiang University HuShugen, Song Xiaowen, Zhang Wei and others carried out the first numericalsimulation of the EQ1118GA Dongfeng flat-head cargo military transportvehicle. After studying the four model schemes, the optimal shroud form wasfinally selected. With an additional device, the influence of the bestaerodynamic modeling on the calculation accuracy is obtained. In 2008, ZhaoYouqun, Ren Bin, and others from Nanjing University of Aeronautics andAstronautics used Fluent software to explore the influence of the rearspoiler on the aerodynamic characteristics of the car from the aspects ofprofile shape, positioning, and angle of attack. In 2011, Hubei Institute ofAutomotive Technology Li Chulin, Li Yan and others performed numericalsimulations on the external flow field of a car body, and analyzed theinfluence of the rear window slope on the aerodynamic performance of the carbody ^[3].

2 The basic content of the design, the objectives,the proposed technical solutions and measures.

2.1 Designbasic content

According to the requirements of automotive bodyaerodynamic design, the basic content of this design includes the followingaspects:

(1) Analyzethe structure and shortcomings of the light car body;

Analyze the current overall shape and structuralcharacteristics of local components of various types of light passenger cars,such as: head height, tail height, hood slope, front window inclination, rearwindow inclination, bumper position, grille shape, etc. And analyze theadvantages and disadvantages of the current body structure modeling.

(2) Analysisand determination of the body structure scheme suitable for light cars;

According to previous analysis of thecharacteristics of body structure, initially identified a good overallaerodynamic property of the body structure, while retaining the basicexterior car body curve on the use of Catia software for three-dimensionalmodel.

(3) Optimizethe aerodynamic characteristics of the light car body and perform simulationanalysis;

Use Fluent and other software to perform numericalsimulation of the three-dimensional external flow field on the previouslyestablished digital model, and obtain aerodynamic factors such as aerodynamiccoefficients, external flow field velocity vector diagrams, pressuredistribution maps, velocity streamlines, and turbulence characteristics ofwake fields Science characteristic parameters.

(4) Partialoptimization design of automobile appearance;

According to the previously obtained parameters, thelocal modeling is continuously optimized.

(5) Comparativeanalysis of the optimization results of the structure of each part;

After the optimization of the parameters wereanalyzed to determine the configuration of each part to optimize the resultsto finalize the best aerodynamic properties obtained styling.

2.2 Designgoals

According to the basic content of the design, thedesign goals are as follows:

(1) Completethe aerodynamic design of the overall body and obtain the design parameters

Through the analysis of the current structuralfeatures of lightweight car body, to determine the basic parameters of bodyshape design.

(2) Obtaina digital 3D model of the car body

The use of modeling software such as Catia, completesimulation of the exterior of the car, get a three-dimensional digital modelof the vehicle body.

(3) Obtainthe external flow field analysis and aerodynamic characteristic parameters ofthe car body

Such as the use of Fluent simulation software,complete digital model designed before the digital simulation of the externalflow field, to get the air car model dynamic characteristics.

(4) Obtainthe results after local optimization design

According to the previously obtained parameters, thelocal optimization design of the car appearance was performed, and theoptimized results were obtained.

(5) Finallyget a good aerodynamic property of the light car styling

Local optimization of the results obtained wereanalyzed and compared, ensuring aesthetic styling of the car, based on the aerodynamicsto get good light sedan body styles.

2.3 Proposed Technical Solutions and Measures

According to the design requirements and thenational standards of the industry, comparing the advantages anddisadvantages of the current light car styling structure, first determine thebasic parameters of the body shape, complete the overall design of the bodyshape, and use Catia software to build the body model. The body model isimported into the simulation analysis software Fluent, and loads are appliedto the simulation model with reference to a variety of actual operatingconditions to obtain the aerodynamic characteristics of the model, therebyverifying whether the car body meets the aerodynamic performance indicatorsand performing local optimization , Establish the optimization model andcontinue the analysis until the optimal model is designed, and the designflow chart is as above.

3 Schedule

Accordingto design requirements, the design of the schedule as shown in Table 3.1