同轴旋转可压缩气体中液体射流及单液滴内空化气泡稳定性研究

发布时间：2018-01-16 00:32

  本文关键词：同轴旋转可压缩气体中液体射流及单液滴内空化气泡稳定性研究　出处：《北京交通大学》2016年博士论文　论文类型：学位论文

  更多相关文章： 旋转 可压缩 空化气泡 热效应 射流 液滴 稳定性 色散方程

【摘要】：液体射流普遍存在于自然界和工程中；在柴油机、缸内直喷汽油机以及燃气轮机等动力机械中,燃油的喷射、分裂雾化及其与空气的混合是实现高效燃烧的基础和前提,对发动机的动力性、经济性以及排放特性等具有重要的影响。燃油射流的分裂与雾化过程,实际上就是液体射流的失稳过程；液体射流稳定性问题一直以来都是内燃机领域的一个研究热点。论文采用理论解析和数值模拟方法对同轴旋转可压缩气体中液体射流分裂与雾化问题进行了研究；研究工作可以进一步完善液体射流及分裂液滴内空化气泡稳定性数学模型,加深对液体射流分裂与雾化机理的理解。建立了描述同轴旋转可压缩气体中液体射流稳定性的色散方程,并考虑了空化气泡的影响；分别给出了时间模式和空间模式下色散方程的数值求解方法。在此基础上,探讨了射流周围气体的同轴旋转以及射流及周围气体的可压缩性对射流轴对称扰动和非轴对称扰动的作用以及对射流稳定性的影响；对射流分裂液滴粒径的计算公式进行了改进；研究了空化气泡的存在所产生的射流物性变化对射流稳定性的作用;对含空泡射流空间模式稳定性与时间模式稳定性的差异以及造成两者之间差异的影响因素进行了分析。通过研究,明确了射流周围气体同轴旋转、射流及周围气体可压缩性以及空化气泡对射流稳定性的作用,含空泡射流空间模式稳定性与时间模式稳定性的差异及其影响因素。给出了存在热效应的液体射流自由表面三维扰动控制方程,得到了扰动压力方程、速度方程和温度方程,建立了描述同轴旋转可压缩气体中液体射流热稳定性的色散方程,并对色散方程及其求解方法进行了验证。在此基础上,进行了存在热效应的同轴旋转可压缩气体中液体射流稳定性分析。通过研究,明确了射流内部温度梯度对液体射流表面扰动波发展的影响,液体射流表面与周围气体间温差对液体射流稳定性的作用。基于非线性稳定性理论,推导出描述液体射流表面扰动的一阶与二阶扰动控制方程,对扰动控制方程进行了解析求解,确定了气液交界面一阶与二阶边界条件；建立了描述同轴旋转可压缩气体中含空泡液体射流非线性稳定性的色散方程,并对色散方程进行了验证分析。在此基础上,进行了射流表面一阶与二阶扰动及其发展的分析,对线性与非线性稳定性理论下的射流形态与分裂进行了比较,进行了同轴旋转可压缩气体中含空泡液体射流非线性稳定性研究。通过研究,明确了射流表面扰动的发展状态,线性与非线性稳定性理论下液体射流的形态及分裂特点,以及射流周围气体的同轴旋转、射流和周围气体的可压缩性以及空化气泡对射流形态及射流分裂长度的影响。在同时考虑空化气泡、分裂液滴及空气粘性的条件下,建立了描述燃油分裂液滴内空化气泡稳定性的色散方程,对色散方程进行了验证分析,并对色散方程的根进行了讨论。在此基础上,从空泡受力角度对空泡的稳定性及其影响因素进行了研究,建立了分裂液滴内空泡临界破碎准则,并应用该准则对分裂液滴内空泡的破碎特性及影响因素进行了分析。通过研究,明确了空化气泡、分裂液滴及空气的粘性对空泡稳定性的影响,空泡惯性力、空泡可压缩性力、液滴内外部气动力以及空泡液滴界面处表面张力对空泡稳定性的作用,以及分裂液滴内空泡的破碎特性及影响因素。基于VOF方法建立了描述液滴内空化气泡生长及溃灭的计算模型,并对数值模拟结果进行了验证分析。在此基础上,通过数值模拟研究,探讨了液滴内空泡生长的控制机理,分析了液滴内空泡生长的影响因素,研究了液滴内空泡溃灭过程及其特征参数的变化规律；在考虑相变的条件下,对空泡溃灭计算模型进行了改进,并在此基础上对存在相变的液滴内空泡的溃灭历程进行了分析。通过研究,揭示了液滴内空泡生长的控制机理,明确了表面张力系数、液滴粘度和液滴密度对空泡生长过程的影响,空泡溃灭过程中溃灭压力、溃灭体积、反弹压力及反弹体积的变化规律,以及存在相变时液滴内空泡的溃灭历程。
[Abstract]:Liquid jet exists widely in nature and engineering; in diesel engine, Disi engine and gas turbine power machinery, fuel injection, atomization and mixing of air is the basis and prerequisite for achieving efficient combustion, the engine power, has an important effect on economy and emission characteristics. The breakup and atomization of the fuel jet, is actually a liquid jet instability process; liquid jet stability problem has been a hot research topic in the field of internal combustion engines. The simulation of the coaxial rotation of breakup and atomization of liquid jet in compressed gases are studied by theoretical analysis and numerical research work can be further used in this paper; improvement of liquid jet and droplet fission in the cavitation bubble stability mathematical model, deepen our understanding of the mechanisms of breakup and atomization of liquid was established to describe the understanding. The dispersion equation of coaxial rotation can stability liquid jet of compressed gas, and the influence of the cavitation bubble; the numerical method for solving the dispersion equation of time and space mode mode are given. Based on this, discusses the surrounding gas jet jet and coaxial rotating and surrounding gas compressibility of axisymmetric jet disturbance and the non axisymmetric disturbances and the influence on the stability of jet; jet droplet size formula has been improved; the jet property change of cavitation bubble produced by the presence of jet stability; influence factors of the difference between the two of physaliferous jet space mode and time stability the difference of stability and mode are analyzed. Through the research, the surrounding gas jet coaxial rotation, jet and the surrounding gas compressibility and air Effect of bubbles on the jet stability, factors of physaliferous jet space mode stability and time stability mode and its influence is given. The control equation of liquid free surface jet 3D disturbance of thermal effect, pressure perturbation equation, velocity equation and temperature equation was established to describe the coaxial rotation dispersion equation of liquid jet thermal stability can be compressed gas, and the dispersion equation and its solving method are verified. Based on this, the stability analysis of liquid jet of compressed gas in rotating coaxial can exist thermal effect were carried out. Through the research, the temperature gradient inside the jet disturbance wave development on the liquid jet surface clear, effect of liquid jet surface and surrounding gas the temperature difference on the liquid jet stability. Nonlinear stability theory based on the first and two description of the liquid jet surface disturbance is derived The control equation of order disturbance, the disturbance control equation is solved analytically, the gas-liquid interface of first order and two order boundary conditions; to describe the coaxial rotation can be dispersion equation with nonlinear stability of cavitation of liquid jet of compressed gas, and the dispersion equation is verified and analyzed. On this basis, the analysis of jet the surface of the one and two order perturbation and the development of the jet shape and splitting of the theory of linear and nonlinear stability were compared, can study on nonlinear stability of coaxial rotating liquid jet cavity containing a compressed gas was carried out. Through the research, clarify the development condition of jet surface disturbance, the morphology and characteristics of the theory of linear split liquid jet with the nonlinear stability, and coaxial jet gas around the rotating jet and the surrounding gas compressibility and cavitation bubbles on the jet morphology and shoot The effect of flow split length. Considering the cavitation bubbles, splitting droplet and viscosity of air conditions, the dispersion equation is established to describe the fuel droplet fission in cavitation bubble stability, the dispersion equation is verified, and the roots of the dispersion equation are discussed. On this basis, the force from the bubble the angle of stability of cavity and its influencing factors were studied. A droplet fission cavity in the critical fracture criterion, crushing factor characteristic and the influence and the application of the criterion of cavitation split within the droplets are analyzed. Through the research, the cavitation bubbles, splitting droplet and air viscosity on bubble stability. Cavitation bubble inertia force, compression force, droplet internal and external aerodynamic and bubble droplet surface tension effect on bubble stability, and crushing characteristics and the impact of droplets within the cavity due to split . calculation model to describe the droplets within the cavitation bubble growth and collapse is established based on the VOF method, and the numerical simulation results are verified and analyzed. On this basis, through numerical simulation, discusses the control mechanism of droplet vacuoles in growth, analyzes the factors influence of droplet vacuoles, variation study on the features and parameters of the liquid droplet in the process of bubble collapse; in considering the transformation conditions, the bubble collapse calculation model is improved, and on the basis of the analysis of the collapse process exist within the bubble droplet phase. Through the research, the control mechanism of droplet vacuoles in growth reveals clear the influence of surface tension coefficient, droplet viscosity and droplet density on the growth process of the bubble, the collapse pressure during the bubble collapse collapse volume variation and rebound rebound pressure volume, and in liquid phase The collapse process drop vacuoles within.

【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TK401
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本文编号：1430794