【作者】 陈明；

【导师】 成艾国； 黄东杰；

【作者基本信息】 湖南大学 ， 车辆工程（专业学位）， 2019， 硕士

【摘要】 随着人民生活水平的不断提升,以及国家路桥等基础建设的飞速发展,汽车成为人们日常生活中的主要代步工具,截至2018年6月底,全国机动车保有量达到3.19亿辆。汽车的大量使用造成了能源的紧缺,因此有效地降低汽车油耗受到更多的关注,而降低汽车风阻系数是降低汽车油耗的一个重要途径。汽车外流场的研究对于汽车风阻系数的降低至关重要,目前汽车外流场的研究方法主要有风洞试验研究和数值仿真研究,其中风洞试验方法具有成本高、周期长等缺点,而随着计算机技术的不断发展,以及湍流计算模型的不断完善,计算流体力学(CFD)在汽车外流场研究中的应用越来越受到国内外学者的重视。但是在汽车外流场数值计算的研究中,目前主要集中在求解方程、求解方法、湍流模型以及网格类型等方面,而对网格划分方式研究较少。本文创造性地提出了网格分区控制技术这一网格划分方法,即根据几何面的特征尺寸大小,以及零部件在外流场分析中的贡献量,对不同零部件采用不同的网格大小进行划分。该技术的应用,旨在保证计算收敛性和准确性的前提下,减少网格数量从而减少计算时间。通过对某车型采用四种不同网格类型(纯四面体、混合四面体、切割体、多面体)的网格划分方法,以验证不同网格类型在汽车外流场中的适用性。结果显示,在相同网格尺寸和网格分区控制条件下,切割体网格的计算结果最贴近试验结果,同时具有网格数量少,网格质量高以及计算时间短等优点。通过对N-S方程及湍流模型的深入研究,本文在数值计算中采用精度较高且占用资源较少的Realizablek-?模型作为湍流模型,结合网格分区控制技术以及切割体网格划分方法,计算结果与吉林大学汽车风洞试验结果高度吻合,风阻系数误差不到1.6%,且局部表面压力误差小于10%,仿真结果具有较高的准确性。本文提出的网格分区控制技术以及网格类型和计算模型的选用提高了汽车外流场仿真结果的准确性,同时大量地节省了汽车外流场仿真中占用的计算资源和时间。文中分析并总结了仿真结果中压力场、速度场以及湍动能的变化规律与汽车表面结构的相互关系,为进一步降低汽车风阻提供有效的理论支持。该技术的应用可进一步提高汽车研发优化效率,对缩短汽车开发周期具有较大的促进作用。更多还原

【Abstract】 With the continuous improvement of people’s living standards and the rapid development of infrastructure such as national roads and bridges,automobiles have become the main vehicle in people’s daily life.By the end of June 2018,the number of automobiles in China had reached 319 million,which has caused a shortage of energy.So how to reduce the fuel consumption of automobiles has been a research hotspots.However,reducing the drag coefficient is an important way to reduce fuel consumption of automobiles.While the external flow field study is very important for the reduction of automobile drag coefficient.At present,the main research methods of automobile external flow field are wind tunnel test and numerical simulation.For the wind tunnel test method,which has the disadvantages of high cost and long period.With the development of computer technology and the improvement of turbulence models,computational fluid dynamics(CFD)has been used in automobile external flow study.However,the main focus fields in the study of numerical simulation of automotive external flow field are solving equations,solving methods,turbulence models and grid types,while the researchs on grid generation methods are less.In this paper,grid partition control technology,a new grid generation method,has been creatively put forward.According to the characteristic size of geometric surface and the contribution of components in the analysis of external flow field,different grid sizes are used for different parts of automobile.The application of this technology aims at reducing the number of grids and computing time on the premise of ensuring the convergence and accuracy of simulation.And four different meshing forms(pure tetrahedron,mixed tetrahedron,trimmer and polyhedron)are used to verify the applicability of different meshing methods in automobile external flow field.The results show that under the same mesh size and mesh partition control conditions,the calculation results of trimmer mesh are closest to the experimental results,and which also have the advantages of fewer meshes,higher mesh quality and shorter computing time.In this paper,Realizablek-?model has been used in the simulation,which has high accuracy and less computer resources occupation.Combining with grid partition control technology and trimmer volume mesh,the simulation result is highly consistent with the experiment result in Jilin Universityautomobile wind tunnel.The deviation of drag coefficient is less than 1.6%,and the deviation of surface pressure is below 10%,which indicate that the result of simulation has a high accuracy.In this paper,the grid partition control technology and the selection of grid type and turbulence model has been proposed,which can improve the accuracy of the simulation results of vehicle external flow field,and save a lot of computing resources and time of simulation.And the relationship between pressure field,velocity field,turbulent kinetic energy and surface structure of automobile is analyzed and summarized,which provides effective theoretical support for further reducing drag coefficient.This technology provides a certain guiding for improving the efficiency of research and design optimization and shortening the development cycle of automobile.更多还原