不同车型车身非光滑表面的气动减阻特性研究与优化

Abstract

With the accelerated construction and popularization of the expressway system, the average speed of automobiles is getting higher and higher,which leads to more pronounced effects of aerodynamic drag and the increase of automobile energy consumption is attracting more and more attention.Related research shows that the aerodynamic drag of a vehicle is approximately proportional to the square of its speed, and every10%reduction in aerodynamic drag can save about4%of fuel.Thus,it can be seen that reducing aerodynamic drag can significantly save fuel consumption and improve fuel economy,and is an important measure to achieve energy conservation and emission reduction of automobiles.With the continuous deepening of research on automotive aerodynamics,the traditional aerodynamic drag reduction method has developed relatively mature and has encountered technical bottleneck,so it is urgent to find some new methods and ideas of aerodynamic drag reduction.Studies have found that the non-smooth surface structure of many organisms in nature tends to have remarkable drag reduction effect,inspired by this,this paper introduces the bionic non-smooth structure into the vehicle body for research,in order to reduce the aerodynamic drag of the vehicle.

In this paper,the CFD numerical simulation method is used and verified by the wind tunnel test.The pit type non-smooth surface is selected as the research object, which is arranged on the top,tail and bottom of different models of Ahmed passenger car model,GTS truck model and stepped back MIRA sedan model respectively,and the influence of the non-smooth surface location on aerodynamic drag reduction effect of different vehicle models is studied by numerical simulation.Then by comparing the key flow field parameters such as wake structure,velocity,wall shear stress,pressure, and turbulent kinetic energy of smooth and tail non-smooth models,the influence of non-smooth surface on the outflow field of different vehicle models is further analyzed, and based on the comparison results of the flow field parameters,the drag reduction mechanism of the tail non-smooth surface is elaborated briefly from the perspective of the drag reduction mechanism of the pressure difference resistance and the friction resistance.After that,the optimization method based on the approximate model is used to optimize the non-smooth surface so that the best combination of parameters can be obtained to make the drag reduction effect optimal.The optimization results show that

optimized non-smooth surface can reach4.69%and5.18%respectively.Finally,the typical external flow field parameters before and after optimization of the two non-smooth models,such as speed,pressure and turbulent kinetic energy are compared and analyzed to further visually demonstrated the feasibility of the optimization method and the reliability of the optimization results.

This paper discusses the influence of the pit type non-smooth structure location on aerodynamic drag reduction effect of different vehicle models,and briefly describes the drag reduction mechanism of the non-smooth structure.Then the main geometric dimensions of the non-smooth structure are optimized by the multi-island genetic algorithm,and the more significant optimization results are obtained.It provides method reference and theoretical guidance for the parameter design and engineering application of the non-smooth surfaces.At the same time,it also provides a new idea for the aerodynamic drag reduction research of different models of passenger cars, trucks and sedans.

Key words：Non-smooth surface；Aerodynamic drag reduction；Optimization design；

Different vehicle models；Wind tunnel test

学位论文原创性声明...............................................................................................................I 摘要.....................................................................................................................................II Abstract....................................................................................................................................III 第1章绪论.. (1)

1.1研究背景及意义 (1)

1.2车辆气动减阻技术的研究概述 (4)

1.2.1被动控制减阻 (5)

1.2.2主动控制减阻 (6)

1.3研究历史和现状 (7)

1.4本文的主要研究内容 (10)

1.5本章小结 (11)

第2章单元体的选取与设计 (12)

2.1湍流边界层相关理论 (12)

2.1.1边界层 (12)

2.1.2拟序结构 (13)

2.2单元体几何形态的选取 (14)

2.3单元体布置位置的选取 (15)

2.4单元体排列方式的选取 (16)

2.5单元体尺寸的确定 (16)

2.6本章小结 (17)

第3章非光滑汽车模型的数值仿真计算 (18)

3.1计算流体力学理论基础 (18)

3.1.1CFD的求解流程 (18)

3.1.2基本控制方程 (19)

3.1.3控制方程的离散 (20)

3.1.4湍流模型 (20)

3.1.5近壁区流场处理 (22)

3.2几何模型的建立 (22)

3.2.1Ahmed模型建立 (22)

3.2.2GTS模型建立 (23)

3.3.1选取计算域 (25)

3.3.2网格划分 (26)

3.4求解参数的设置 (28)

3.4.1湍流模型选择 (28)

3.4.2边界条件与求解器设置 (29)

3.5风洞试验验证 (30)

3.6数值仿真计算结果对比 (31)

3.7本章小结 (32)

第4章非光滑表面对不同车型外流场的影响 (33)

4.1非光滑表面对Ahmed模型外流场的影响 (33)

4.1.1尾流结构对比分析 (33)

4.1.2气流速度对比分析 (34)

4.1.3壁面剪应力对比分析 (36)

4.1.4压力对比分析 (37)

4.1.5湍动能对比分析 (37)

4.2非光滑表面对GTS模型外流场的影响 (38)

4.2.1尾流结构对比分析 (38)

4.2.2气流速度对比分析 (39)

4.2.3壁面剪应力对比分析 (41)

4.2.4压力对比分析 (41)

4.2.5湍动能对比分析 (42)

4.3非光滑表面对阶梯背MIRA模型外流场的影响 (43)

4.3.1尾流结构对比分析 (43)

4.3.2气流速度对比分析 (44)

4.3.3壁面剪应力对比分析 (46)

4.3.4压力对比分析 (46)

4.3.5湍动能对比分析 (47)

4.4非光滑表面减阻机理分析 (48)

4.4.1压差阻力减小机理分析 (48)

4.4.2摩擦阻力减小机理分析 (48)

4.5本章小结 (49)

第5章尾部凹坑非光滑表面优化设计 (50)

5.1基于近似模型的优化设计方法 (50)

5.1.3优化算法 (52)

5.2Ahmed与GTS模型尾部非光滑表面优化设计 (53)

5.2.1优化问题描述 (54)

5.2.2试验设计 (54)

5.2.3近似模型建立 (56)

5.2.4优化设计 (57)

5.3优化结果分析 (57)

5.3.1优化前后气流速度对比分析 (57)

5.3.2优化前后压力对比分析 (59)

5.3.3优化前后湍动能对比分析 (60)

5.4本章小结 (61)

总结与展望 (62)

1.总结 (62)

2.展望 (63)

参考文献 (65)

致谢 (69)

附录A（攻读学位期间发表的论文） (70)