基于FLUENT的汽车气动特性分析与减阻研究

发布时间：2018-04-01 08:23

本文选题：SUV　切入点：FLUENT　出处：《重庆交通大学》2016年硕士论文

【摘要】：无论是对于传统的燃油汽车还是当今的电动汽车,“节能环保”是汽车设计的永恒主题。当前世界各国面临严峻的石油危机,加上汽车电池关键技术无法突破,使得石油这种不可再生资源暂时无法被完全被电能取代,因此设计低阻汽车具有重要意义。随着我国汽车工业的发展,自主品牌汽车的崛起,汽车速度有了较大提升。有研究表明,汽车速度越快,风阻越大,燃油消耗也越多,良好的车身外形能够有效的减少汽车阻力,提升汽车的燃油效率。本文以某紧凑型SUV为原型,在CATIA中建立三维曲面模型,然后在ICEM中进行非结构四面体网格的划分,将网格文件导入FLUENT中,采用Realizable k-?湍流模型和标准近壁面函数以进行高精度模拟,最后将计算结果文件导入TECPLOT中进行后处理。首先,本文介绍了无侧风作用下汽车外流场的模拟流程,并计算得到气动阻力系数和气动升力系数。然后对横摆角β分别为6deg、12deg、18deg、24deg和30deg的五种侧风工况进行模拟,模拟结果表明侧风作用下汽车的气动特性跟无侧风的相比有很大的不同,随着横摆角的增大,汽车的三个气动力系数均会不同程度的增大,尤其以气动侧向力系数增幅最大。然后利用CATIA的数字建模技术,选取了对汽车外形影响较大的五个关键结构参数,分别为:前风窗角、后风窗角,前部上翘角,离地间隙和尾部上翘角。然后将它们进行了五因素四水平共16个模型的正交试验,试验得出了各个因素的最优水平,将它们组合在一起得到优化模型,同时试验结果表明后风窗角和离地间隙是对汽车气动阻力影响程度最大的两个因素。然后将最优模型的四个因素固定,研究其中一个因素的变化对气动阻力的影响。最后对优化模型进行模拟计算发现阻力系数0.3506,比原车模型降低了6.98%,通过分析其速度分布图,压力分布图和湍动能分布图并与原车模型对比,发现优化模型的气动特性得到改善,找到了阻力系数减低的原因。最后在正交优化模型的基础上,对其进行了二次优化,设置了8deg的前脸倾角,把发动机盖圆角半径由200mm增大到300mm,仿真结果表明,二次优化模型的阻力系数下降到0.3425,比正交优化模型降低了2.3%。本论文优化取得了良好的效果。
[Abstract]:Energy saving and environmental protection are the eternal themes of automotive design, both for traditional fuel vehicles and electric vehicles today. Countries in the world are facing a severe oil crisis, and the key technologies of automotive batteries cannot be broken through. The non-renewable resources such as petroleum can not be completely replaced by electric energy, so it is of great significance to design low-resistivity vehicles. With the development of automobile industry in China, the rise of self-owned brand cars. Some studies have shown that the faster the speed of the car, the greater the wind resistance, the more fuel it consumes, and the better the shape of the body can effectively reduce the resistance of the car. In this paper, a compact SUV is used as the prototype, a 3D surface model is built in CATIA, then the unstructured tetrahedron mesh is divided in ICEM, the grid file is imported into FLUENT, and Realizable k-? The turbulence model and the standard near-wall function are used for high-precision simulation. At last, the result file is imported into TECPLOT for post-processing. Firstly, the simulation process of the automobile outflow field without cross-wind is introduced in this paper. The aerodynamic drag coefficient and the aerodynamic lift coefficient are calculated, and then the aerodynamic characteristics of the vehicle under crosswind action are different from those of the non-cross wind, when the yaw angle 尾 is 6 degg 12degg 18 degg 24deg and 30deg, respectively, the simulation results show that the aerodynamic characteristics of the vehicle are different from those of the non-cross wind, and the results show that the aerodynamic characteristics of the vehicle are different from those of the non-cross wind. With the increase of the yaw angle, the three aerodynamic coefficients of the vehicle will increase to some extent, especially the aerodynamic lateral force coefficient. Then the digital modeling technology of CATIA is used. Five key structural parameters, which have great influence on the automobile shape, are selected: the front wind window angle, the rear wind window angle, the front upwarping angle, the front wind window angle, the rear wind window angle, and the front wind window angle. Then the orthogonal experiments of 16 models with five factors and four levels were carried out, and the optimal level of each factor was obtained, and the optimized model was obtained by combining them together. At the same time, the test results show that the rear wind window angle and the clearance from the ground are the two most influential factors on the aerodynamic resistance of the vehicle. Then the four factors of the optimal model are fixed. The influence of one of the factors on the aerodynamic resistance is studied. Finally, the simulation of the optimization model shows that the drag coefficient is 0.3506, which is 6.98 lower than the original model. Compared with the original vehicle model, the pressure distribution diagram and turbulent kinetic energy distribution map show that the aerodynamic characteristics of the optimization model are improved, and the reasons for the reduction of the drag coefficient are found. Finally, the quadratic optimization is carried out on the basis of the orthogonal optimization model. The front face inclination angle of 8deg is set, and the radius of engine cover rounded angle is increased from 200mm to 300mm. The simulation results show that the resistance coefficient of the quadratic optimization model is reduced to 0.3425, which is 2.3 less than that of the orthogonal optimization model. Good results have been obtained in this paper.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U461.1

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