本文選題：微型客車 + 尾氣排放模擬方案　； 參考：《湖南大學(xué)》2016年碩士論文

【摘要】：近年來,隨著汽車保有量逐年提高,導(dǎo)致能源危機與尾氣擴散污染空氣質(zhì)量的問題日益凸顯,提高汽車燃油經(jīng)濟性和控制尾氣擴散規(guī)律已成為國內(nèi)外汽車廠商研究的前沿和熱點,而這些問題的有效解決都離不開汽車空氣動力學(xué)的研究,因此,以降低汽車氣動阻力及控制尾氣擴散規(guī)律為目的的汽車氣動特性研究具有重要的實際意義。目前,汽車空氣動力學(xué)的氣動阻力特性優(yōu)化主要通過車身的流線形設(shè)計和局部造型改進等方法來實現(xiàn)。由于汽車受到造型,工藝,成本的限制,這些方法降低阻力的空間越來越小,所以,必須尋找其它減阻途徑,進一步改善汽車的氣動阻力特性。研究表明,尾渦是產(chǎn)生氣動阻力特性的主要因素,而汽車在行駛過程中尾氣排放會影響尾渦,且尾氣排放由尾氣管結(jié)構(gòu)決定,同時汽車在高怠速行駛工況下,尾氣排放劇增且不易擴散,對行人呼吸帶區(qū)域的空氣質(zhì)量污染最為嚴(yán)重,這也跟尾氣管的設(shè)計密切相關(guān)。因此研究尾氣管的設(shè)計對氣動阻力特性和尾氣擴散特性的影響具有重要的實際意義,但二者之間存在復(fù)雜的耦合關(guān)系,而多學(xué)科設(shè)計優(yōu)化(Multidisciplinary Design Optimization,簡稱MDO)通過不同目標(biāo)之間的協(xié)同效應(yīng),從而獲得整體滿意解,在航空航天領(lǐng)域已得到長足發(fā)展和廣泛應(yīng)用,在汽車設(shè)計領(lǐng)域的研究才剛剛起步。所以基于協(xié)同優(yōu)化方法綜合考慮尾氣減阻特性和尾氣擴散特性之間的耦合關(guān)系,避免優(yōu)化設(shè)計中只考慮單個性能的片面性,具有重要的理論意義和工程價值。本文以數(shù)值仿真計算為重點,其次結(jié)合風(fēng)洞試驗,從汽車氣動特性的角度出發(fā),對某微型客車的尾氣減阻特性和尾氣擴散特性進行了研究,并在此基礎(chǔ)上運用協(xié)同優(yōu)化方法設(shè)計了一種低阻,低污染的尾氣管結(jié)構(gòu)。主要研究內(nèi)容如下:1.以試驗數(shù)據(jù)為依據(jù),從仿真計算精度和計算效率出發(fā),對比分析了不同湍流模型和網(wǎng)格策略對尾氣排放數(shù)值模擬的適應(yīng)性,選擇了最優(yōu)的湍流模型和網(wǎng)格策略,最終確定了一套適用于尾氣排放的數(shù)值模擬方案。2.提出了基于尾氣排放控制尾渦的減阻方法,并驗證其可行性。通過CFD仿真計算,得到了尾氣管在不同排氣速度,不同形狀,不同位置,不同角度下尾氣減阻的變化規(guī)律,在此基礎(chǔ)上,還提出了基于尾氣脈動排放來實現(xiàn)減阻的方式。最后,通過瞬態(tài)計算,詳細(xì)對比分析了尾氣定常排放和尾氣脈動排放的減阻機理。3.確定行人呼吸帶的范圍,運用組分輸運模型研究了尾氣管在不同排氣速度,不同形狀,不同位置,不同角度下的尾氣擴散特性對行人呼吸帶的影響,并得到了相應(yīng)規(guī)律。4.綜合考慮尾氣減阻特性和尾氣擴散特性,提出了一種新型尾氣管排放,運用協(xié)同優(yōu)化方法對尾氣管結(jié)構(gòu)參數(shù)進行優(yōu)化,同時為了提高優(yōu)化效率,基于一種計算流體力學(xué)與優(yōu)化算法相集成的技術(shù),得到了一種既能減阻又能減少尾氣擴散對行人呼吸帶影響的尾氣管結(jié)構(gòu)。
[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.

【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：U461.1

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