气体旋转运动对环膜液体射流不稳定性影响的研究

环膜液体射流的破碎机理研究对于GDI汽油机的雾化过程具有重要的意义。利用线性不稳定性理论研究了旋转气体运动对低阶和高阶模式黏性环膜液体射流破碎的影响。对于色散方程的数值计算结果表明,无论是对称模式还是非对称模式,低阶模式的扰动增长率通常较之高阶模式要大得多,但较之低阶模式扰动,高阶模式对气体旋转运动更为敏感。研究结果同时表明,对于非对称模式,无论是低阶模式还是高阶模式的扰动,气体旋转运动都是液体破碎的失稳因素;对于对称模式,气体旋转运动是低阶模式扰动的促稳因素,然而却是高阶模式扰动的强烈的失稳因素。     

二甲醚射流雾化的不稳定性研究

利用线形稳定性理论,推导出可用来描述粘性射流表面扰动发展所满足的色散方程,并进行了无量纲化处理,利用该色散方程对二甲醚射流在正常条件和闪急沸腾条件下的不稳定性进行了研究.结果表明,在正常喷射条件下,提高射流速度和减小液体粘度可促进二甲醚射流的雾化效果,而表面张力和环境气体密度对射流不稳定性的影响则相对复杂;在闪急沸腾喷射条件下,闪急沸腾效应越明显,二甲醚射流越不稳定.     

液体燃料射流最不稳定频率的理论分析（1）——液体燃料射流的最不？…

利用线性不稳定性理论,对粘性液体燃料射流射入气体介质的射流模型所对应的色散方程进行了数值求解。利用计算结果,分析了液体燃料射流不稳定性研究中的３个最重要的无量纲参数参韦韦伯数Ｗｅ、雷诺数Ｒｅ及密度比Ｑ,对分别处于瑞利模式和泰勒模式下的液体射流的最不稳定频率及对应的最大扰动增长率的影响。     

实际射流参数对加热条件下液体燃料射流不稳定性的影响

利用线性热不稳定性理论,对黏性液体射入高温气体介质所对应的色散方程进行了数值求解．利用所得到的计算结果,研究了加热条件下射流速度、气液密度比、液体黏度、温度梯度及液体种类等实际射流参数对射流最大扰动增长率及占优波数的影响规律．研究结果表明：对于加热条件下Reyleigh模式的液体射流,气液密度比、温度梯度是射流破碎的失稳因素,而射流速度、液体黏度则是液体射流破碎的促稳因素;对于Taylor模式的液体射流,射流速度、温度梯度、气液密度比是射流破碎的失稳因素,而液体黏度是液体射流破碎的促稳因素．研究结果同时证明了液体种类的改变对射流不稳定性的影响是多种因素共同作用的结果．     

液体燃料射流最不稳定频率的理论分析(1)--液体燃料射流的最不稳定频率及无量纲数的影响

利用线性不稳定性理论,对粘性液体燃料射流射入气体介质的射流模型所对应的色散方程进行了数值求解.利用计算结果,分析了液体燃料射流不稳定性研究中的3个最重要的无量纲参数韦伯数We、雷诺数Re及密度比Q,对分别处于瑞利模式和泰勒模式下的液体射流的最不稳定频率及对应的最大扰动增长率的影响.结果表明,在不同的射流模式下,这3个无量纲数对液体射流最不稳定频率的影响是不同的,在这两种射流模式下,射流系统具有不同的频率特征.     

加热条件下液体燃料射流破碎机理的研究

利用线性热不稳定性理论,对黏性液体射入高温气体介质模型所对应的色散方程进行了数值求解。利用所得到的计算结果,研究了加热条件下轴对称模式扰动液体射流破碎机理,探讨了表征各种影响射流破碎作用力的无量纲Weber数（We）、密度比（Q）、Marangoni数（Ma）和Ohnesorge数（Z）对液体射流破碎最大扰动增长率及占优波数的影响。研究结果表明,液体和气体介质之间的温度梯度对液体射流稳定性有着非常显著的影响,表明热毛细力对于液体射流的破碎有促进作用,这种作用对处于Taylor模式下的液体射流尤为显著,并且这种热力作用可使液体射流从一种模式进入另一种模式,并可以大大改变射流的破碎尺序。     

液体燃料射流破碎的热不稳定性分析

利用线性不稳定性理论,基于基本控制方程和边界条件,获得了表征黏性液体射流射人高温气体介质的射流不稳定性所对应的色散方程,并对该方程进行了数值求解,根据计算结果,分析了若干因素对加热条件下Reylei曲模式和Taylor模式液体射流热不稳定性的影响,结果表明,对上述两种模式的液体射流,由温度梯度引起的热毛细力是促进射流破碎的重要原因,并且这种作用在Taylor模式液体射流中表现更为显著。     

同轴旋转可压缩气体中液体射流形态

基于非线性稳定性理论,在同时考虑射流周围气体同轴旋转、射流和周围气体可压缩性以及射流液体中含空化气泡的条件下,建立了描述同轴旋转可压缩气体中含空泡液体射流稳定性的色散方程,并验证了色散方程及其求解方法的正确性.在此基础上,进行了同轴旋转可压缩气体中含空泡液体射流形态的研究.结果表明:周围气体的同轴旋转改变了射流表面的占优扰动模式,即扰动模式由轴对称扰动占优转变为非轴对称扰动占优;随着气体同轴旋转强度的增加,射流周向形态的变化越来越明显,射流表面会逐渐形成越来越多凹凸不平的波纹.射流及其周围气体的可压缩性对射流周向形态的影响不明显,但会对射流的轴向形态产生一定作用.总体上看,空泡的存在对射流形态的影响弱于气体同轴旋转的影响.通过研究进一步完善了液体射流稳定性数学模型,加深了对液体射流分裂与雾化机理的理解.     

液体燃料射流最不稳定频率的理论分析(2)--射流参数对最不稳定频率的影响及试验观察

利用对色散方程的数值计算结果,分析了实际射流参数如射流速度、液体种类、喷孔半径、液体粘度、介质压力等对分别处于瑞利模式和泰勒模式下的液体射流的最不稳定频率及其最大扰动增长率的影响.结果表明,在不同的射流模式下,实际射流参数对液体射流最不稳定频率的影响是不同的.并对受激液体射流现象进行了初步试验观察.     

液体燃料射流量不稳定频率的理论分析（2）——射流参数对最不稳定？…

利用对色散方程的数值计算结果，分析了实际射流参数如射流速度，液体种类，喷孔半径，液体粘度，介质压力等对分别处于瑞利模式和泰勒模式下的液体射流的最不稳定频率及其最大扰动增长率的影响。结果表明，在不同的射流模式下，实际射流参数对液体射流最不稳定频率的影响是不同的。并对受激液体射流现象进行了初步试验观察。     

高速粘性液体射流的不稳定模式

本利用线性不稳定性理论研究了高速粘液性射流的破碎问题，并利用先进的高速分幅全息摄影技术首次比较系统地观察了几种不稳定模式的表明形态，实验观察结果与理论预测基本一致。研究结果表明，在适当的条件下，非轴对称模式也有可能成为最不稳定模式，从而肯定了非轴对称模式在射流破碎中的重要作用。     

Confined Boiling Heat Transfer,Two-Phase Flow Patterns,and Jet Impingement in a Hele-Shaw Cell

ABSTRACT

Experiments were carried out to study heat transfer and two-phase flow patterns during boiling in a Hele-Shaw cell filled with pure water vapor at atmospheric pressure and with a central inlet of a liquid jet. The Hele-Shaw cell was based on a circular copper rod surface and a polycarbonate plate permitting optical access and thus high-speed cinematography. The diameter of the heated copper rod was 10 mm, the jet diameters were 0.5 and 1 mm, and spacing was varied between 50, 100, and 200 μm. The heat was applied through 4 cartridge heaters with a maximum heat flux of 327 W/cm². Results showed how high-volume flow rates for the liquid jet led to jet impingement heat transfer while low flow rates led to a Hele-Shaw flow boiling system. The relationship between the volume flow rate and the temperature difference differed significantly between these two regimes. Different flow patterns and evaporation fronts were observed using high-speed cinematography. They strongly depended on jet properties, applied heat flux, and gap spacing. The efficiency of the Hele-Shaw flow boiling system during high heat flux levels was attributed to high interface velocities, combined with viscous fingering at the interface. This combination led to high wetting rates with substantial microlayer evaporation. Good results regarding the heat transfer and the pressure drop were obtained with the final configuration of a 10-mm copper rod diameter, a jet diameter of 1 mm, and a spacing of 0.1 mm. A rather surprising observation was the existence of a stable rotation of an evaporating liquid jet in the Hele-Shaw boiling chamber. The driving mechanism for the rotation with a frequency of 105 Hz was the rapid microlayer evaporation at the rear side of the rotating liquid jet.     

Internal flow in evaporating droplet on heated solid surface

This work numerically studies the evaporation process of a liquid droplet on a heated solid surface using a comprehensive model. The internal flow within the evaporating liquid droplet is elucidated, while considering the effects of buoyancy force, thermocapillary force, and viscous resistance. The evaporation process is modeled by simultaneously solving the Navier–Stokes equations and energy equation for the liquid domain and the heat conduction equation for the solid domain, while assuming the liquid–vapor interface is a free surface. Three dimensionless parameters are utilized to describe the contribution of individual driving forces to internal flow. Evolutions of the thermal and internal flows during evaporation are discussed. The volume evolution and experimental data are in good agreement.     

液体射流的非轴对称破碎

本文分析粘性液体射流的线性稳定性问题，本文首次根据理论预测所确定的物理条件观察到了射流在各种非轴对称模式支配下的破碎情况，实验采用的是高速公路分幅激光全息技术，实验结果表明，液体射流结构遵守稳定性理论所预测的规律，实验还发现，液体射流的实际破碎尺寸要大于线性稳定必伯预测结果。     

柴油机多阶雾化模型及动态喷雾模拟

本文在作者推导的有粘液柱３维不稳定弥散关系式的基础上，对柴油机喷注的雾化机理进行了分析，建立了燃油雾化的多阶不稳定模型，根据不稳定流的最大波幅增长点提出了初始雾化参数（如滴径及滴径分布，喷雾锥角）的具体算法，并考虑了液滴的２次雾化问题。以半波正弦喷油规律为例的动态喷雾模拟表明，本文的计算对蒸发量有明显的改进，从而有助于解决原ＫＩＶＡ计算中蒸发量不足的问题，更重要的是，初始雾化模型的建立把多维模型中缸内工作过程与缸外供油过程密切联系起来，有利于分析喷油系统对喷雾混合过程的影响。     

Comprehensive experimental and theoretical study of fluid flow and heat transfer in a microscopic evaporating meniscus in a miniature heat exchanger

The complex physicochemical phenomena occurring in the contact line region of an evaporating meniscus are described using a unique combination of high-resolution experimental data and three complementary models. The following were used: (1) high-resolution experimental liquid profile data (thickness, slope, curvature and curvature gradient) to obtain the pressure gradient in the evaporating pentane meniscus in a vertical constrained vapor bubble (VCVB); (2) macroscopic outside surface temperature profile data; (3) a finite element model to obtain the two-dimensional heat conduction profile in the solid substrate wall (macro-model) and the solid–liquid interfacial temperature profile in the evaporating meniscus region; (4) a continuum fluid-dynamics model (micro-model) to obtain the liquid–vapor interfacial temperature, mass flow rate, Marangoni stresses, and evaporative heat flux profiles along the length of the evaporating meniscus; and (5) the Kelvin–Clapeyron model to obtain the vapor temperature profile (liquid–vapor interfacial temperature jump) in the evaporating meniscus region.The retarded dispersion constant and high-resolution thickness, slope, curvature and curvature gradient profiles were obtained from the experimental reflectivity profiles. There was a substantial increase in the measured curvature in the transition region, where the evaporation rate and flux are a maximum. To obtain numerical closure between the three complementary models, the continuum fluid dynamics model (micro-model) required slip at the solid–liquid interface to support the observed high mass flow rates in the evaporating pentane meniscus. Mass flow rates due to Marangoni stresses, capillary pressure and disjoining pressure are compared. Depending on the liquid thickness, Marangoni stresses can either enhance or hinder fluid flow towards the contact line for the evaporating pure pentane meniscus. Due to the high heat removal rate by the evaporating pentane meniscus in the transition region, dips in the vapor, liquid–vapor and solid–liquid interface temperature were obtained. The results demonstrate and describe the sensitivity and complexity of the phase change process in micro-regions.