扩散型气柱界面R-M失稳中混合率的实验研究

发布时间：2018-06-05 16:00

本文选题：扩散型界面 + R-M不稳定性　；参考：《力学学报》2016年05期

【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.
[Abstract]:Richtmyer-Meshkov-R-M) instability exists in many engineering problems, and shock tube experiment is the main method to study R-M instability. The planar laser-induced fluorescence technique has molecular tracer ability and can obtain the interfacial gas concentration (molar fraction) distribution, which provides a powerful tool for the study of the interfacial instability mixing problem. In the experiment of impact-diffusion gas column interface, the mixing problem of SF6-Air interface caused by R-M instability was studied by PLIF technique. By changing the long-axis ratio of the elliptical initial interface, the molar fraction of gas in the evolution process of three diffusion-type initial interfaces is obtained. The phenomena of simple tension, secondary instability and extrusion jet are observed under baroclinic mechanism. The instantaneous mixing rate of the interface is obtained by using the concentration distribution. Through the instantaneous mixing rate, the overall average mixing rate of the interface and the probability density distribution of the mixing rate, the interfacial mixing characteristics at different evolution stages are analyzed. The mechanism of interfacial instability mixing is discussed. In the early stage of evolution, the interface was stretched and curled under the action of baroclinic vortices, and the mixing of the interface was promoted by increasing the concentration gradient. With the further development of evolution and the emergence of secondary instability, the interfacial turbulent mixing state is achieved by small scale convection, while the intermolecular mixing driven by concentration gradient weakens gradually. There is a "competitive" relationship between the diffusion caused by the concentration gradient and the convection caused by the secondary instability, both of which dominate the interfacial mixing.
【作者单位】：中国工程物理研究院流体物理研究所冲击波物理与爆轰物理国防科技重点实验室;
【基金】：国家自然科学基金资助项目(11172278,11302201,11472253)
【分类号】：O354.5

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