汽车尾气减阻特性和扩散特性的协同优化研究

发布时间：2018-05-07 05:19

本文选题：微型客车 + 尾气排放模拟方案　；参考：《湖南大学》2016年硕士论文

【摘要】：近年来,随着汽车保有量逐年提高,导致能源危机与尾气扩散污染空气质量的问题日益凸显,提高汽车燃油经济性和控制尾气扩散规律已成为国内外汽车厂商研究的前沿和热点,而这些问题的有效解决都离不开汽车空气动力学的研究,因此,以降低汽车气动阻力及控制尾气扩散规律为目的的汽车气动特性研究具有重要的实际意义。目前,汽车空气动力学的气动阻力特性优化主要通过车身的流线形设计和局部造型改进等方法来实现。由于汽车受到造型,工艺,成本的限制,这些方法降低阻力的空间越来越小,所以,必须寻找其它减阻途径,进一步改善汽车的气动阻力特性。研究表明,尾涡是产生气动阻力特性的主要因素,而汽车在行驶过程中尾气排放会影响尾涡,且尾气排放由尾气管结构决定,同时汽车在高怠速行驶工况下,尾气排放剧增且不易扩散,对行人呼吸带区域的空气质量污染最为严重,这也跟尾气管的设计密切相关。因此研究尾气管的设计对气动阻力特性和尾气扩散特性的影响具有重要的实际意义,但二者之间存在复杂的耦合关系,而多学科设计优化(Multidisciplinary Design Optimization,简称MDO)通过不同目标之间的协同效应,从而获得整体满意解,在航空航天领域已得到长足发展和广泛应用,在汽车设计领域的研究才刚刚起步。所以基于协同优化方法综合考虑尾气减阻特性和尾气扩散特性之间的耦合关系,避免优化设计中只考虑单个性能的片面性,具有重要的理论意义和工程价值。本文以数值仿真计算为重点,其次结合风洞试验,从汽车气动特性的角度出发,对某微型客车的尾气减阻特性和尾气扩散特性进行了研究,并在此基础上运用协同优化方法设计了一种低阻,低污染的尾气管结构。主要研究内容如下:1.以试验数据为依据,从仿真计算精度和计算效率出发,对比分析了不同湍流模型和网格策略对尾气排放数值模拟的适应性,选择了最优的湍流模型和网格策略,最终确定了一套适用于尾气排放的数值模拟方案。2.提出了基于尾气排放控制尾涡的减阻方法,并验证其可行性。通过CFD仿真计算,得到了尾气管在不同排气速度,不同形状,不同位置,不同角度下尾气减阻的变化规律,在此基础上,还提出了基于尾气脉动排放来实现减阻的方式。最后,通过瞬态计算,详细对比分析了尾气定常排放和尾气脉动排放的减阻机理。3.确定行人呼吸带的范围,运用组分输运模型研究了尾气管在不同排气速度,不同形状,不同位置,不同角度下的尾气扩散特性对行人呼吸带的影响,并得到了相应规律。4.综合考虑尾气减阻特性和尾气扩散特性,提出了一种新型尾气管排放,运用协同优化方法对尾气管结构参数进行优化,同时为了提高优化效率,基于一种计算流体力学与优化算法相集成的技术,得到了一种既能减阻又能减少尾气扩散对行人呼吸带影响的尾气管结构。
[Abstract]:In recent years, with the increase of automobile ownership year by year, the problem of energy crisis and air pollution caused by exhaust diffusion has become increasingly prominent. Improving the economy of automobile fuel and controlling the diffusion of exhaust gas has become the frontier and hot spot of automobile manufacturers both at home and abroad, and the effective solution of these problems can not be separated from the research of automobile aerodynamics. Therefore, it is of great practical significance to study the aerodynamic characteristics of automobile in order to reduce the aerodynamic drag of automobile and to control the law of exhaust gas diffusion. At present, the aerodynamic drag characteristic optimization of automobile aerodynamics is realized mainly through the streamline design of the body and the improvement of the local modeling. It is limited that the space for reducing resistance is getting smaller and smaller, so other ways of reducing drag must be found to further improve the aerodynamic drag characteristics of a car. The study shows that the tail vortex is the main factor to produce aerodynamic drag characteristics, and the exhaust emission of the vehicle will affect the tail vortex during the driving process, and the exhaust emission is determined by the tail pipe structure. Meanwhile, the exhaust gas emission is determined by the tail gas pipe structure. At high idle speed, the exhaust emission increases dramatically and is not easy to spread. The air quality pollution of the pedestrian breathing zone is most serious, which is closely related to the design of the tailpipe. Therefore, it is of great practical significance to study the effect of the design of the tail gas on the aerodynamic drag characteristics and the emission characteristics of the tail gas, but there is a complex relationship between the two. Multidisciplinary design optimization (Multidisciplinary Design Optimization, abbreviated as MDO) obtains the overall satisfactory solution through the synergy between different targets, which has been developed and widely used in the aerospace field, and the research in the field of automotive design is just starting. Considering the coupling relationship between the tail gas drag reduction characteristic and the tail gas diffusion characteristic, it is of great theoretical significance and engineering value to avoid only one sidedness of single performance in the optimization design. This paper focuses on the numerical simulation calculation and then combines the wind tunnel test to reduce the exhaust gas of a minibus from the angle of the aerodynamic characteristics of the car. The characteristics of resistance and tail gas diffusion are studied. On this basis, a kind of low resistance and low pollution exhaust pipe structure is designed by using the cooperative optimization method. The main contents are as follows: 1. based on the experimental data, the exhaust emission number of different turbulence models and grid strategies is compared and analyzed on the basis of the simulation accuracy and calculation efficiency. The optimal turbulence model and grid strategy are selected, and a set of numerical simulation schemes for exhaust emission is determined by.2.. The method of drag reduction based on tail vortex control of exhaust emission is proposed and its feasibility is verified. The exhaust gas velocity, different shapes and different positions of the tailpipe are obtained by CFD simulation. On the basis of this, the method of reducing drag based on exhaust gas pulsation is proposed on this basis. Finally, through transient calculation, the drag reduction mechanism of tail gas constant emission and tail gas pulsation emission reduction mechanism.3. determines the range of pedestrian breathing zone, and the exhaust pipe is studied by using the component transport model. The effect of exhaust diffusion characteristics on the pedestrian breathing zone at different exhaust speeds, different shapes, different positions, and different angles, and the corresponding law.4. comprehensive consideration of the characteristics of tail gas drag reduction and tail gas diffusion, a new type of exhaust pipe emission is proposed, and the structure parameters of the tail gas pipe are optimized by using the synergistic optimization method, at the same time, the structure parameters of the tail gas pipe are optimized. In order to improve the optimization efficiency, a kind of tail gas pipe structure, which can reduce the drag and reduce the effect of tail gas diffusion on the pedestrian breathing zone, is obtained based on the technique of integrating the computational fluid dynamics and the optimization algorithm.

【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U461.1

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