【作者】 李博；

【导师】 周哲玮； 胡国辉；

【作者基本信息】 上海大学 ， 流体力学， 2008， 博士

【摘要】 喷射雾化是上世纪七十年代发展起来的一项冶金工艺,由于它能够生产高性能的冶金产品,近年来在世界各地得到了广泛和快速发展。其中,超音速气体雾化技术由于生成的产品质量较好而得到了较多的研究和关注。这项技术的关键之处在于它能够产生高频振动的超音速气流,其中高频振动的产生原因是由于超音速气体雾化喷嘴内Hartmann共振管结构的存在。因此,对Hartmann共振管中高频振动的产生机理的研究是对超音速气体雾化喷嘴内共振现象进行研究的基础。近年来,由于Hartmann共振管装置在流动的主动控制方面的应用得以广泛开展,对其共振原理的研究也随之得到了非常多的关注。其中,核心问题也是亟待解决的问题,是Hartmann共振管在几种共振模式之间转换的机理问题,以及随之带来的共振管工作的稳定性问题。但由于问题本身的困难程度,到目前为止,它还没有得到彻底的解决。对于超音速气体雾化喷嘴内部流场的研究开展得比较有限,对其的两个重要功能:高频脉动气流和超音速气流的产生机理的理论和数值研究目前在文献中还未见到,鉴于这项技术正日益得到重视和应用,因此,对其的研究具有重要性和现实意义。本论文中,首先通过对前人相关研究的调研和总结,介绍了Hartmann共振管现象的发现和理论、实验、数值模拟的研究进展,并重点介绍了Brocher等人(1970)提出的对于回流模式的“有限循环”理论,作为计算工作的理论依据和参照。本文中的计算工作主要分为两个部分:(一)Hartmann共振管流场的数值模拟(1)采用基于Roe解法的有限体积法,对Hartmann共振管流场进行了数值模拟,首先通过对一个Hartmann共振管的基本算例的数值模拟,分析了流场在回流模式下振动时流场结构的变化过程,研究了压缩波和膨胀波在管内的传播和反弹及向外场传播的过程,讨论了振动随共振管管长和射流马赫数的变化趋势,将结果同理论和实验趋势相对照,验证了计算结果对于物理问题的正确性。(2)首次研究和分析了激励器作用下共振管共振模式的转换及其机理。并将本文的研究和前人的研究相结合,探讨了激励器对振动促进作用主要的三个方面:1.放宽了回流模式振动的产生对物理参数的要求;2有助于振动在回流模式下的产生和保持.;3.有效提高了振动强度。(二)超音速气体雾化喷嘴(USGA喷嘴)流场的数值模拟(1)采用同样的数值方法,对超音速气体雾化喷嘴(USGA喷嘴)流场进行了数值模拟,研究了USGA喷嘴内的共振现象,分析了气流在USGA喷嘴内的共振管和二级共振管结构中的往复流动过程以及压缩波和膨胀波在两管内的传播和反弹的过程,对USGA喷嘴内气流振动的产生机理进行了研究和解释,即喷嘴内的Hartmann共振管和二级共振管在回流模式下振动的共振。通过对数值结果的研究,探讨了二级管对流场的振动所起的促进作用,这主要体现在两方面,即共振效应和对回流模式的促进作用,并研究了振动随管长及射流马赫数的变化趋势。(2)通过数值模拟研究了超音速气体雾化喷嘴中的“自适应喉部”的形成及其造成的气流从亚音速向超音速转变的现象,解释了造成这一现象的原因是由于出流导管壁面附近的涡结构的存在,并用数值结果呈现了自适应喉部结构的所在位置和流场结构。(3)通过数值结果推断了USGA喷嘴内的共振现象和自适应喉部现象产生的临界马赫数的大小。对于USGA喷嘴内的流场振动的研究和对超音速脉动气流产生的机理分析在前人的文献中从未见到,对于工程应用具有指导意义。更多还原

【Abstract】 Spray atomization is a metallurgic technology developed in the 1970s.Because of its capability of producing high quality metallurgic products,the technology has been been developed quickly and extensively worldwide.Ultra-sonic gas atomization particularly attracted more research and attentions due to superior products quality. The key to this technology is that it can generate high frequency pulsating ultra-sonic gas flow which is caused by existence of Hartmann resonance tube structure in ultra-sonic gas atomization nozzle.Therefore,research on mechanism of generation of high frequency oscillation in Hartmann resonance tube is the foundation of research on resonance phenomenon in ultra-sonic gas atomization nozzle.In recent years,as Hartmann resonance tube device is widely applicated in active flow control,extensive attentions have been attracted to the principle of resonance.The key and impending problem is the mechanism of Hartmann resonance tube shifting between several resonance modes as well as working reliability of resonance tube along with it. However,until now the problem has not been totally solved due to its difficulty. Research on flow field inside ultra-sonic gas atomization nozzle is comparatively limited.Theoretical and numerical research on mechanism of the generation of its two major functions,hitch frequency pulsating gas flow and ultra-sonic gas flow could not be seen in current literature.As this technology is being increasingly valued and applied,research on it is important and practical.In this dissertation,firstly previous related research is summarized and research progress on discovery,theory,experiments and numerical simulation of Hartman resonance tube phenomenon is introduced.Limit circle theory for the jet regurgitant mode raised by Brocher(1970)is emphasized as theoretical foundation and reference of computation.Computational work of this dissertation mainly consists of two parts:Ⅰ.Numerical simulation of flow in the Hartmann resonance tube(1)Finite volume method based on Roe solver is adopted to conduct numerical simulation for Hartmann resonance tube flow field.Through numerical simulation of a basic computational case of Hartmann resonance tube,evolution of flow field in the jet regurgitant mode is analyzed,process of propagation,reflection of compression wave and expansion wave inside the tube and propagation toward external flow field are studied.Variation trends of oscillation along with resonance tube length and jet Mach number are discussed and the results are compared with theoretical and experimental trends to validate the computational results for physical problems.(2)For the first time,resonance mode shifting and its mechanism of resonance tube under influence of actuator is studied and analyzed.Research in this dissertation is combined with work of previous researchers to probe into the three main aspects of oscillation strengthening by actuator:1.Requirement for physical parameters for the generation of oscillation in the jet regurgitant mode is mitigated;2 Favorable for generation and maintenance of oscillation in the jet regurgitant mode;3.Oscillation intensity is effectively enhanced.Ⅱ.Numerical simulation of flow in the ultra sonic gas atomization nozzle(1)The same numerical method is adopted to conduct numerical simulation for flow in the ultra-sonic gas atomization(USGA)nozzle.Resonance phenomenon in USGA nozzle is studied,and reciprocating gas flow in resonance tube and secondary resonance tube structure inside USGA nozzle and propagation and reflection process of compression wave and expansion wave in the two tubes are analyzed.Generation mechanism of pulsating gas flow inside USGA nozzle is studied and explained,that is the resonance of oscillations in Hartman resonance tube and secondary resonance tube in the jet regurgitant mode.By studying numerical results,strengthening of flow field oscillation by secondary tube is analyzed,which mainly demonstrates in two aspects, resonance effect and strengthening of jet regurgitant mode.Variation trends of oscillation along with resonance tube length and jet Mach number are also studied.(2)The formation of "self-adjusting throat" in the USGA nozzle and the consequent phenomenon of the trasition of gas flow from subsonic to supersonic are studied by numerical simulation.The reason for this phenomenon is explained by the exsistence of vortex structure adhering on the wall of outflow duct.The location and flow structure of the self-adjusting throat are represented by numerical results.(3)The critical jet Mach numbers of the occurrences of resonance phenomenon and self-adjusting throat phenomenon in the USGA nozzle are speculated by numerical results.The study of the flow oscillation in the USGA nozzle and the analysis of the mechanism of generation of supersonic pusating gas flow have not been seen in previous literature.The study acts as the guidance for practical application.更多还原