摘要
Richtmyer-Meshkov(R-M)不稳定性普遍存在于众多工程问题中,激波管实验是研究R-M失稳问题的主要手段.高精度的平面激光诱导荧光(planar laser-induced fluorescence,PLIF)技术具有分子量级的示踪能力,可获得界面气体浓度(摩尔分数)分布,为研究界面失稳混合问题提供了有力工具.在弱激波(Ma=1.25)冲击扩散型气柱界面实验中,采用PLIF技术对R-M失稳引起的SF6-Air界面混合问题进行了研究.通过改变椭圆形初始界面的长短轴比,得到了3种扩散型初始界面失稳演化过程中气体摩尔分数,观察到了斜压机制下界面的简单拉伸、二次不稳定性、挤压射流等现象.利用浓度分布进一步得到了界面的瞬时混合率,通过瞬时混合率、界面整体平均混合率以及混合率的概率密度分布,分析了界面在不同演化阶段的界面混合特征,初步讨论了界面失稳混合的机制.演化初期,界面在斜压涡的作用下发生拉伸卷曲,通过增大浓度梯度来促进界面的混合.当演化进一步发展,二次不稳定性出现后,界面通过小尺度对流的方式达到湍流混合状态,而浓度梯度驱使的分子间混合逐渐减弱.由浓度梯度引起的扩散与由二次不稳定性引起的对流存在着"竞争"关系,二者共同主导了界面的混合.
Richtmyer-Meshkov（R-M） instability has attracted extensive attention in many engineering application fields.Shock tube experiment is a widely used technique in the study of R-M instability. Thanks to the molecular-level traceability, planar laser-induced fluorescence（PLIF） diagnostic technique offers concentration（mole fraction） map of interface gas with high resolution. It shows the way to study the mixing in the instability evolution. Diffuse gas cylinder interfaces are accelerated by a weak shock wave（Ma = 1.25） in the experiment. Using PLIF, the mixing of interface is investigated,which is induced by R-M instability. By changing the aspect ratio of elliptic cylinder, concentration maps of diffuse gas cylinders with three types of initial configurations are obtained. The simple stretching, the secondary instability and the jet caused by extrusion in the concentration field are clearly revealed. Moreover, the mixing rate of different stages of evolution is calculated from concentration field. Attempting to understand the mechanism of mixing, instantaneous mixing rate, total mixing rate of the interface and the probability density distribution of mixing rate are analyzed in detail. At early time, baroclinic vorticity accelerates the mixing through stretching interface and intensifying concentration gradient.As the evolution develops, the secondary instability appears, causing the flow transitions to turbulence as a result of smallscale convection. At meantime, molecular mixing induced by concentration gradient is weakened. There is a competitory relationship between diffusion caused by concentration gradient and convection caused by secondary instability, which control the mixing together.
作者
黄熙龙
廖深飞
邹立勇
刘金宏
曹仁义
Huang Xilong Liao Shenfei Zou Liyon g Liu Jinhong Cao Renyi(National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, CAEP, Mianyang 621900, Sichuan, China)
出处
《力学学报》
EI
CSCD
北大核心
2016年第5期1073-1079,共7页
Chinese Journal of Theoretical and Applied Mechanics
基金
国家自然科学基金资助项目(11172278,11302201,11472253)
