【作者】 刘江；

【导师】 兰巍；

【作者基本信息】 吉林大学 ， 机械工程（工业设计工程）（专业学位）， 2020， 硕士

【摘要】 汽车已成为人们日常生活中不可或缺的一部分,从满足基本的代步需求到追求更高品质的需要使得人们对汽车各方面性能的要求越来越高。汽车在雨天高速行驶时,雨水和汽车相互作用使得前风窗与侧窗通常会出现一定程度的视野受阻问题,这对于高速行驶的汽车安全至关重要,严重时会发生惨烈的交通事故导致生命和财产的重大损失。前风窗视野问题可通过汽车雨刮器解决,侧窗上的污染通常来自前风窗雨刮器排水与后视镜影响,较难解决。因此,研究汽车在雨天行驶时的侧窗污染来源与污染规律、通过有效的设计减轻侧窗水相分布具有非常必要的理论意义与工程应用价值。本文采用格子玻尔兹曼方法求解流场结构,而流场中液滴运动轨迹与车身表面液膜的沉积与流动分别利用离散相模型与欧拉壁面液膜模型求解,详细考虑了液滴与车身可能发生的一系列现象如液滴破裂、飞溅、再夹带等,保障了数值模拟的准确性。通过对DrivAer模型的多相流数值模拟,分析了汽车前风窗及侧窗的污染过程,探索A柱溢流机理,并对A柱溢流现象进行控制。仿真结果表明除了A柱溢流污染,侧窗还存在大量由于后视镜影响而造成的雨水污染,该污染主要由于不合理的后视镜造型设计对流场形成扰动,导致携带液滴的气流对侧窗造成冲刷形成污染,并将其归纳为三种污染来源。为更好地分析和评价后视镜对侧窗造成污染影响,将侧窗进行区域划分,并建立评价标准R_C值作为衡量污染轻重的定量指标。得出后视镜对侧窗的污染机理后,本文从后视镜造型因素出发,进行了十种造型因素对侧窗污染的研究,分别为后视镜三角基座尾部挡板、有无基座、后视镜镜柱长度、尺寸、安装位置、后视镜镜罩迎风角度、内侧扩散角、前缘倒角、后缘离去角、后脸深度,通过改变各因素改变流场结构从而影响液滴运动轨迹,并对其中多种因素进行其尺寸上的影响规律探索。通过各因素对侧窗污染影响研究,探索各因素之间的相互关系和综合效果,得到能够改善侧窗污染的有效方案,并对其中几种进行组合,得到优化后视镜模型。结果显示侧窗底部象限污染R_C值仅为0.211,相比原模型总体减小41.4%,但低于各因素改善比例之和,说明各因素之间存在耦合作用关系。最后对该优化模型和原模型进行了不同速度与不同降雨量工况下的性能评估,以验证该模型的适用性,结果表明该优化方案在速度较高、雨量较大时仍然具有较好的改善效果。本文探索了一套基于格子玻尔兹曼方法与离散相模型的用于研究汽车前风窗、侧窗污染现象的数值仿真方法,分析和揭示了不同后视镜造型因素对于侧窗污染影响机理,深入探索了各因素尺寸对侧窗污染的影响规律。本文的研究方法和结论对汽车后视镜研发与改善雨天汽车侧窗污染具有一定的借鉴价值,为今后学者研究与企业车型开发提供了参考。更多还原

【Abstract】 Automobiles have become an indispensable part of people’s daily life.People’s requirements for automobiles’performance from the need for basic mobility to the pursuit of higher quality are getting higher and higher.When the automobile is driving at high speed,the interaction of rain and vehicle makes the driver’s front windscreen and side window usually have a water obstruction of vision,which is very important for the safety.In severe cases,catastrophic traffic accidents will lead to significant loss of life and property.The problem of the front windscreen visibility can be solved by the vehicle wiper.The contamination on the side window usually comes from the drainage of the wiper and the influence of the rearview mirror.Therefore,it is of great theoretical and practical significance to study the contamination sources and contamination laws of side windows,and to reduce the rain contamination of side windows through effective design.The Lattice Boltzmann method is used for turbulence modeling;DPM model is selected for droplet trajectory tracking and Eulerian wall films model is selected for water film accumulating and moving on body surface.A series of phenomenon that may occur between the droplet and the vehicle surface,such as droplet break-up,splash,and re-entrainment are considered to ensure the accuracy of numerical simulation.The contamination process of the front windscreen and side window is achieved after simulation.The phenomenon of A-pillar overflow is controlled to explore the mechanism of A-pillar overflow.The results show that in addition to the A-pillar overflow contamination,there is still a lot of water contamination caused by the influence of the rearview mirror in the side window.It is mainly due to the unreasonable rearview mirror shape design that disturbs the flow field,which causes the airflow carrying droplets to scour the side window.In order to better analyze and evaluate the impact of rearview mirror on the contamination of side window,the side window is divided into several regions,and the evaluation standard R_C value is established as a quantitative index to measure the severity of contamination.After the contamination mechanism is obtained,ten types of rearview mirror styling factors are established to study the side window contamination,which can change the flow field structure and finally affect the droplet trajectory.Through the simulation,an effective scheme to improve the contamination of side windows is obtained,and several effective factors are combined to obtain an optimized rearview mirror model to explore the correlation and comprehensive effects of various factors.The results show that the R_C value of the side window bottom quadrant is only 0.211,which is41.4%lower than the original model,but lower than the sum of the improvement ratios of all factors,indicating that there is a coupling relationship between the factors.Finally,the optimization model and the original model are evaluated for EWM performance under different speeds and rainfall conditions to verify the applicability of the model.The results show that the optimization model still has good performance at high speed and heavy rain conditions.This paper explores a numerical simulation method based on Lattice Boltzmann method and discrete phase model for studying the contamination of front windscreen and side window of automobiles,analyzes and reveals the influence of different rearview mirror styling factors on side window contamination.And the effects of the size of each factor on the contamination of side windows are explored.The research method and results have important guidance and reference value for the future research and design of rearview mirrors.更多还原