重/轻单模界面的Richtmyer-Meshkov不稳定性研究

Study on Richtmyer-Meshkov instability at heavy/light single-mode interface

本文采用实验与数值相结合的方法研究平面激波冲击重/轻单模界面的Richtmyer-Meshkov(RM)不稳定性问题,着重分析重/轻型界面和轻/重型界面演化的差异.实验上,利用先进的肥皂膜界面生成方法,生成初始形状可控的SF6/air单模界面,并基于高速纹影技术捕捉界面和波系的详细演化过程.数值上,采用可压缩多组分流动高精度数值模拟程序对实验工况进行模拟,数值模拟结果和实验结果吻合良好,详细的数值流场信息促进了我们对实验中界面分层现象的分析和理解.研究发现,与轻/重界面演化不同的是,重/轻界面在激波冲击后首先进入反相阶段;与轻/重界面演化类似的是,反相后的重/轻界面依次经历线性和非线性发展.最后,本文利用实验获得的定量数据检验已有线性和非线性模型对重/轻RM不稳定性的预测能力,发现Meyer&Blewett模型(Phys.Fluids,1972,15:753–759)能有效预测重/轻界面的线性期扰动增长,而Dimonte&Ramaprabhu模型(Phys.Fluids,2010,22:014104)能有效预测非线性期的扰动增长.

The Richtmyer-Meshkov(RM)instability at a heavy/light single-mode interface is studied both experimentally and numerically in this work,focusing on the interface structure evolution and the perturbation amplitude growth.The difference between the RM instability of the heavy/light interface and the light/heavy case(J.Fluid Mech.,2018,853:R2)is discussed.Experimentally,an advanced soap film technique is adopted to generate an SF6/air gaseous interface with a controllable shape such that the instability development can be accurately examined.Detailed evolutions of the interface morphology and the wave pattern are captured by a high-speed video camera combined with schlieren photography.It is observed that the interfacial morphology presents an evident stratification after the phase inversion of the interface(the bubble(spike)reverses to be a spike(bubble)),which is mainly ascribed to the droplet cloud produced by the rupture of the soap film impacted by an incident shock wave.Numerically,a high-order accurate solver for compressible multi-phase flow,which has been thoroughly validated in previous shock-interface interaction studies,is employed to simulate the present heavy/light RM instability.The numerical results show good agreements with the experimental ones,which enables us to perform a detailed flow analysis.Different from the light/heavy case,after the shock impact,the heavy/light interface immediately enters the phase reversal process.After the phase reversal,the interface experiences successively the linear and nonlinear growths,which is similar to the light/heavy case.The reliable experimental and numerical results here allow us to examine the validity of the previous linear and nonlinear models for the heavy/light RM instability growth.It is found that the linear model of Meyer&Blewett(Phys.Fluids,1972,15:753–759)gives a good prediction of the perturbation growth at linear stage up to a dimensionless time of 0.7,and the empirical model of Dimonte&Ramaprabhu(Phys.Fluids,2010,22:014104)reasonably predicts the perturbation growth at the nonlinear stage,which is different from the light/heavy case where the model of Zhang&Guo(J Fluid Mech.,2016,786:47–61)gives the best prediction as suggested by an elaborate experimental study.Our study may facilitate the thorough understanding of the heavy/light RM instability and also can serve as a benchmark for new models.