【作者】 刘娟；

【导师】 王振国；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2012， 博士

【摘要】 本文以气体作用下锥形液膜和圆柱射流破碎过程为研究对象，研究了气体对液体燃料破碎的影响。在研究锥形液膜破碎时，以某型燃气发生器中使用的气液同轴离心式喷嘴为研究对象，从热试试验中选择燃烧性能和燃烧效率较高的一种喷嘴作为基准构型，采用理论、试验、仿真相结合的研究方法，系统地研究了锥形液膜的产生、发展以及破碎过程，在此基础上改变喷嘴的结构参数，研究结构参数对旋转锥形液膜产生、发展的影响。在研究圆柱射流破碎时，以实际使用的气液同轴剪切式喷嘴为对象，对比了有/无气体作用时的破碎过程。设计了透明喷嘴，利用界面追踪Volume of Fluid(VOF)方法模拟了基准喷嘴内部填充过程。液体进入喷嘴后，向切向口上下低压区填充，并将喷嘴内部的气体排挤出喷嘴，气相区的真空度不断增大，当液相流出喷嘴后，内部流场建立，液相填充旋流室和收缩段的时间占整个填充时间的大部分。分析了稳定后喷嘴内部速度、压力场，结果表明液相流经等直段时，轴向速度增加，切向速度减小，在收缩段和等直段存在较大的压力损失。利用大量的冷试试验获得喷嘴流量系数以及喷嘴出口喷雾图像，编制图像处理界面测量雾化锥角，定义无量纲影响因子衡量喷嘴结构参数对喷嘴性能的影响，得到了考虑喷嘴几何特性参数A、旋转直径比Ds/d0和长径比L0/d0等结构参数在内的流量系数以及雾化锥角表达式，补充了基于Abromvich理论的离心喷嘴设计准则。测量了离心式喷嘴在不同结构参数下的雾化粒径，通过改变喷嘴结构参数，基于Reitz的雾化粒径公式，得到了考虑喷嘴旋转直径比Ds/d0，喷嘴长径比L0/d0以及出口扩张角在内的雾化粒径表达式，为喷嘴设计和数值仿真中的初始条件给定提供了参考。设计了喷雾切刀，能够将喷雾锥一部分液体从流场中排开，排除了相对两侧液膜的干扰，尤其在喷嘴出口及高喷注压降工况下效果更明显。利用高速阴影系统、背光试验系统等多种试验方法观测了旋转锥形液膜一次破碎形态，在低韦伯数We下，液膜表面呈现穿孔破碎形态，在高韦伯数We下，液膜表面呈现湍流破碎形态。基于matlab图像处理功能编写了图像处理程序，定义不同轴向位置的液体含量获得液膜表面一次破碎特征。通过对阴影图像处理测量了液膜破碎长度；通过对喷雾切刀作用下的液膜破碎图像进行处理得到了液膜破碎时表面波长，统计得到锥形液膜雾化粒径SMD与破碎时表面波长之间的定量关系。改变喷嘴构型，基于Han的破碎长度公式得到适用于离心式喷嘴使用的破碎长度公式，公式中的破碎长度系数与喷嘴几何特性参数关系较大。利用平面片光技术观察了有/无气体作用时旋转锥形液膜破碎的形态特征，发现大液滴存在于锥形液膜边界，小液滴被空气卷入喷雾锥内部。利用互相关算法得到了液膜破碎后的速度场，在喷雾锥内部，径向速度沿着远离喷雾锥的方向不断增大。旋转锥形液膜喷雾锥中心的速度较小，两侧速度较大，呈现U型分布；锥形液膜在环缝气流作用下，小液滴不断被加速，喷雾锥中心速度较高，向两侧逐渐减小随后又增大，呈现W型分布。利用高速摄影观察了低喷注压降下的圆柱射流破碎形态，呈现波动破碎和剥离破碎两种形态，通过定量测量获得了雾化粒径SMD与表面波长之间的关系。通过对两种液体燃料破碎形式的比较可知，气体加入后，加剧了液体的不稳定，促进了液体表面扰动波的发展，使得液体断裂破碎位置提前；同时气体的加入为流场注入了能量，增加了流场的湍流强度以及液滴的速度，加快了由于湍流引起的液滴输运，雾化后的液滴直径都有减小。更多还原

【Abstract】 This dissertation aimed at the liquid conical sheet and liquid jet breakup processaffected by coflowing gas. When studying the liquid conical sheet breakup process, thegas-liquid coaxial injector adopted by a type of gas generator was chosen. The baselinegeometry of the injector was selected from the hot tests in which it behaved best.Theorical analysis, experimental study and numerical simulation were combinedtogether to study the formation, the development and the breakup of the swirl conicalsheet. Different geometry parameters were analyzed to investigate their influence on theswirl conical sheet. When studying the liquid column jet breakup process, the actualliquid coaxial shear injector was chosen and the primary breakup characteristics wereinvestigated under lower pressure drop.A transparent injector was designed to study the filling process of the liquid phasein the pressure swirl injector. Interface tracking method Volume of Fluid (VOF) wasused to simulate the flow field inside the injector. The liquid phase enters the tangentialinlets, oppressing the gas phase out of the injector. When the liquid phase flows out ofthe injector, the flow field inside the injector is established. It takes a majority of thetotal filling time to occupy the swirl chamber and the convergent section. The velocityand pressure field were also analyzed. The tangential velocity of the liquid phasedecreases when it passes the orifice section. Most of the total pressure loss exsits in theconvergent section and orifice section.Many cold tests were carried out to study the parameter influence on the injectorperformance, including the discharge coefficient, the spray cone angle and the SauterMean Diameter (SMD). The spray cone angle was measured using the image processingprogramme to analyze images of the spray at the exit of the injector. A non-dimensionalparameter was defined to do a quantitive evaluation of geometry parameters’influence on the spray performance. Finally, new formule of the discharge coefficient,the spray cone angle and the SMD were deduced, which consider the geometryparameter A, the ratio of the diameter of the swirl chamber to that of the central post,and ratio of the length of the central post to the diameter of the central post and othergeometry parameters. The new formule give some refrences in the pressure swirlinjector design and supply the initial condtition of the numerical simulation of the gasgenerator.A spray cutter was designed to improve the back-illumination method, which canexclude the interaction between the liquid on the opposite sides of the conical liquidsheet. The spray cutter behaves better under the high pressure drop operating condition.Different methods, including the high-speed shadowgraph, and the high-speedback-illumination combined with the spray cutter, were used to investigate the breakupprocess of swirl conical liquid film. The surface of the conical liquid sheet breaks upwith the perforation pattern at lower Weber number, and with turbulent fragmentation patten at larger Weber number.Image proceeding codes were programmed to measure the primary breakupcharacteristics of the swirl conical liquid film. A non-dimensional parameter wasdefined to evaluate the liquid fraction at different distance to the exit of the injector. Thebreakup length was achieved through the high-speed shadowgraph images and thewavelength was got through the high-speed photography images with the spray cutter.The relationship between the breakup length and Weber number, also the wavelength atthe breakup point with the Weber number were achieved. Finally, the breakup lengthformula was achieved based on Han’s formula. The coefficient of the breakup lengthhas much to do with the geometry characteristic parameters of the pressure swirlinjector.The laser sheet technique was used to investigate the breakup process of swirlconical sheet with the coaxial gas. Larger droplets lie at the boundary of the liquid sheet,smaller droplets are enrolled by the surrounding gas into the center of the spray. Thecross-correlation algorithm was used to compute the flow field. Inside the primarybreakup region, the velocity at the center of the conical spray is smaller than that at theconical spray boundary. The velocity profile appears as U-patter. The radial velocity iscentrosymmetric, increases as the coordinate increases. Affected by the coflowing gas,the smaller droplets are accelerated more markedly than the larger ones. From the centerof the conical sheet to the spray boundary, the velocity of droplets decreases firstly, thenincreases. The velocity profile appears as W-patter.High speed photography was used to study the breakup process of gas-liquidcoaxial shear injector. Two kinds of breakup mechanism were found. One is the wavebreakup, the other is the peeling mechanism. The relationship between SMD and thewavelength at breakup point was deduced.When gas was added around the liquid, the liquid surface tends to be more instableand the liquid phase breakup earlier. Meanwhile, the turbulent intensity increases, whichaugments the turbulence transport and the SMD minishes correspondingly.更多还原