Successive Picket Drive for Mitigating the Ablative Richtmyer–Meshkov Instability

The ablative Richtmyer–Meshkov instability(ARMI) is crucial to the successful ignition implosion of the inertial confinement fusion(ICF) because of its action as the seed of the Rayleigh–Taylor instability. In usual ICF implosions, the first shock driven by various foots of the pulses plays a central role in the ARMI growth. We propose a new scheme for refraining from ARMI with a pulse of successive pickets. With the successive-picket pulse design, a rippled capsule surface is compressed by three successive shocks with sequentially strengthening intensities and ablated stabilization, and the ablative Richtmyer–Meshkov growth is mitigated quite effectively.Our numerical simulations and theoretical analyses identify the validity of this scheme.     

Nonequilibrium kinetics effects in Richtmyer–Meshkov instability and reshock processes

Kinetic effects in the inertial confinement fusion ignition process are far from clear. In this work,we study the Richtmyer–Meshkov instability and reshock processes by using a two-fluid discrete Boltzmann method. The work begins by interpreting the experiment conducted by Collins and Jacobs(2002, J. Fluid Mech. 464, 113–136). It shows that the shock wave causes substances in close proximity to the substance interface to deviate more significantly from their thermodynamic equilibrium state. The ...     

Weakly Nonlinear Rayleigh–Taylor Instability in Cylindrically Convergent Geometry

The Rayleigh–Taylor instability(RTI) in cylindrical geometry is investigated analytically through a second-order weakly nonlinear(WN) theory considering the Bell–Plesset(BP) effect. The governing equations for the combined perturbation growth are derived. The WN solutions for an exponentially convergent cylinder are obtained. It is found that the BP and RTI growths are strongly coupled, which results in the bubble-spike asymmetric structure in the WN stage. The large Atwood number leads to the large deformation of the convergent interface. The amplitude of the spike grows faster than that of the bubble especially for large mode number m and large Atwood number A. The averaged interface radius is small for large mode number perturbation due to the mode-coupling effect.     

Experimental study of initial condition dependence on turbulent mixing in shock-accelerated Richtmyer–Meshkov fluid layers

Experimental evidence is needed to verify the hypothesis that the memory of initial conditions is retained at late times in variable density flows. If true, this presents an opportunity to “design” and “control” late-time turbulence, with an improved understanding in the prediction of inertial confinement fusion and other general fluid mixing processes. In this communication, an experimental and theoretical study on the effects of initial condition parameters, namely, the amplitude δ₀ and wavenumber κ₀ , where λ₀ is the initial wavelength) of perturbations, on late-time turbulence and mixing in shock-driven Richtmyer–Meshkov (R-M) unstable fluid layers in a 2D plane is presented. Single and multi-mode membrane-free initial conditions in the form of a gas curtain having a light-heavy-light configuration (air-SF₆-air) with an Atwood number of A= 0.57 were used in our experiments. A planar shock wave with a shock Mach number M= 1.21 drives the R-M instability, and the evolution of this instability after incident shock is captured using high resolution simultaneous planar laser induced fluorescence (PLIF) and particle image velocimetry (PIV) diagnostics. Time evolution of statistics such as amplitude of the mixing layer, 2D turbulent kinetic energy, Reynolds number, rms of velocity fluctuations, probability density functions, and density-specific volume correlation were observed to quantify the amount of mixing and understand the nature of turbulence in this flow. Based on these results, it was found that the R-M mixing layer is asymmetric and non-Boussinesq. There is a correlation between initial condition parameters and large-scale, and small-scale mixing at late times, indicating an initial condition dependence on R-M mixing.     

A new type of the evolution of the bubble front in the Richtmyer–Meshkov instability

We study the coherent motion of bubbles and spikes in the Richtmyer–Meshkov instability. The theoretical solutions capturing the interplay of harmonics in the nonlinear dynamics are found, and a new type of the evolution of the bubble front is predicted.     

Jet-Like Long Spike in Nonlinear Evolution of Ablative Rayleigh–Taylor Instability

We report the formation of jet-like long spike in the nonlinear evolution of the ablative Rayleigh-Taylor instability （ARTI） experiments by numerical simulations. A preheating model k（T） = KSH[1＋f（T）], where KSH is the Spitzer Harm （SH） electron conductivity and f（T） interprets the preheating tongue effect in the cold plasma ahead of the ablative front [Phys. Rev. E 65 （2002） 57401], is introduced in simulations. The simulation results of the nonlinear evolution of the ARTI are in general agreement with the experiment results. It is found that two factors, i.e., the suppressing of ablative Kelvin Helmholtz instability （AKHI） and the heat flow cone in the spike tips, contribute to the formation of jet-like long spike in the nonlinear evolution of the ARTI.     

Simulation of the Weakly Nonlinear Rayleigh–Taylor Instability in Spherical Geometry

The Rayleigh-Taylor instability at the weakly nonlinear(WN) stage in spherical geometry is studied by numerical simulation.The mode coupling processes are revealed.The results are consistent with the WN model based on parameter expansion,while higher order effects are found to be non-negligible.For Legendre mode perturbation Pn(cos B),the nonlinear saturation amplitude(NS A) of the fundamental mode decreases with the mode number n.When n is large,the spherical NSA is lower than the corresponding...     

Interface Width Effect on the Weakly Nonlinear Rayleigh–Taylor Instability in Spherical Geometry

Interface width effect on the spherical Rayleigh–Taylor instability in the weakly nonlinear regime is studied by numerical simulations.For Legendre perturbation mode P_n with wave number K_n and interface half-width L,the commonly adopted empirical linear growth rate formula γ_n^em(L)=γn/√1 + K_nL is found to be sufficient in spherical geometry.At the weakly nonlinear stage,the interface width affects the mode coupling processes.The development o...     

基于强度介质Richtmyer-Meshkov不稳定性理论的微缺陷喷射模型

采用二维多介质欧拉弹塑性流体动力学程序,对金属界面Richtmyer-Meshkov不稳定性和物质喷射进行流体动力学模拟分析,得到强度效应对界面扰动增长和物质喷射的影响特征,揭示扰动增长与物质喷射之间的内在联系.基于理想弹塑性固体界面Richtmyer-Meshkov不稳定性理论,建立强度介质微喷射形成临界判据、喷射总量和最大速度的理论模型.     

任意Atwood数Rayleigh-Taylor和 Richtmyer-Meshkov 不稳定性气泡速度研究

本文将Layzer气泡模型推广到任意界面Atwood数情形,得到了自洽的微分方程组.该模型描述了气泡从早期的指数增长阶段到气 泡以渐近速度上升的非线性阶段的发展过程,给出了Rayleigh-Taylor(RT)和Richtmyer-Meshkov(RM)不稳定性的二维和 三维气泡速度渐近解,还求出了二维和三维RT不稳定性气泡顶点附近速度的解析解.     

偏心对汇聚激波诱导的RM不稳定性影响的数值研究

数值研究汇聚激波与四种形状（圆形、小振幅单模、大振幅单模和正方形）的二维气柱界面相互作用,激波汇聚中心与界面同心和不同心（即偏心）时Richtmyer-Meshkov（RM）不稳定性的发展规律,重点考察界面中心的压力及混合区面积在两种情况下随时间的变化.数值方法使用VAS2D程序,该方法采用有限体积法结合网格自适应技术,能够达到时间和空间的二阶精度.结果表明,偏心情况下RM不稳定性是其在同心情况下的扰动和偏心小扰动叠加的结果.在本文采用的偏心程度下（20%）,偏心对于圆形无扰动界面发展的影响主要表现在后期界面出现微小扰动结构;而对于单模和正方形这种原本有扰动的界面,偏心使扰动结构呈现不对称及扭曲,同时也影响了界面中心压力和混合区面积,因而加剧了不稳定性的发展.     

Multiple-Relaxation-Time Lattice Boltzmann Approach to Richtmyer-Meshkov Instability

The aims of the present paper are twofold. At first, we further study the Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) model proposed in [Europhys. Lett. 90 (2010) 54003]. We discuss the reason why the Gram-Schmidt orthogonalization procedure is not needed in the construction of transformation matrix M; point out a reason why the Kataoka-Tsutahara model [Phys. Rev. E 69 (2004) 035701(R)] is only valid in subsonic flows.The von Neumann stability analysis is performed. Secondly, we carry out a preliminary quantitative study on the Richtmyer-Meshkov instability using the proposed MRT LB model. When a shock wave travels from a light medium to a heavy one, the simulated growth rate is in qualitative agreement with the perturbation model by Zhang-Sohn. It is about half of the predicted value by the impulsive model and is closer to the experimental result. When the shock wave travels from a heavy medium to a light one, our simulation results are also consistent with physical analysis.     

在非线性三波耦合的不稳定饱和过程中出现的Lorenz型混沌

我们证明了在等离子体中，三波耦合方程同构于Ｌｏｒｅｎｚ型方程，预言了在此过程中会出现Ｌｏｒｅｎｚ型混沌     

Nonlinear saturation amplitude of cylindrical Rayleigh Taylor instability

The nonlinear saturation amplitude （NSA） of the fundamental mode in the classical Rayleigh-Taylor instability with a cylindrical geometry for an arbitrary Atwood number is analytically investigated by considering the nonlinear corrections up to the third order. The analytic results indicate that the effects of the initial radius of the interface （r0） and the Atwood number （A） play an important role in the NSA of the fundamental mode. The NSA of the fundamental mode first increases gently and then decreases quickly with increasing A. For a given A, the smaller the ro/λ（λ is the perturbation wavelength）, the larger the NSA of the fundamental mode. When ro/λ is large enough （r0 〉〉 λ）, the NSA of the fundamental mode is reduced to the prediction in the previous literatures within the framework of the third-order perturbation theory.     

非理想流体中Rayleigh-Taylor和Richtmyer-Meshkov不稳定性气泡速度研究

在随气泡顶端运动的坐标系中, 通过将理想流体模型推广到非理想流体的情况, 研究了流体黏性和表面张力对Rayleigh-Taylor (RT)和Richtmyer-Meshkov (RM)不稳定性气泡速度的影响. 首先得到了RT和RM不稳定性气泡运动的控制方程 (自洽的微分方程组); 其次给出了二维平面坐标和三维柱坐标中气泡速度的数值解和渐近解, 并定量分析了流体黏性和表面张力对RT和RM气泡速度和振幅的影响. 结果表明: 从线性阶段到非线性阶段的全过程中, 非理想流体中的气泡速度和振幅小于理想流体中的气泡速度和振幅. 也就是说, 流体黏性和表面张力对RT和RM不稳定性的发展都具有致稳作用. 关键词： Rayleigh-Taylor不稳定性 Richtmyer-Meshkov不稳定性 气泡速度 非理想流体     

爆轰驱动Cu界面的Richtmyer-Meshkov扰动增长稳定性

研究了爆轰驱动Cu界面的扰动增长过程,分析了不同初始条件下的扰动增长规律和主要失稳机制.研究结果表明:温度相关的熔化失稳和塑性变形相关的拉伸断裂失稳是界面扰动增长过程的主要失稳机制;高能炸药爆轰驱动Cu材料界面时,冲击波加载引起的温升和扰动增长阶段塑性功转换引起的温升不足以熔化Cu材料,拉伸断裂是导致扰动增长不稳定的主要机制;扰动增长非线性阶段尖钉的最大累积有效塑性应变与尖钉振幅之间存在定标关系,结合熔化条件和断裂应变判据建立的尖钉振幅失稳条件可用于分析界面扰动增长的稳定性.     

受激拉曼散射对非线性介质波导的时空不稳定性影响

基于非线性包络方程我们研究了平面非线性介质波导中的时空不稳定性,得到了有拉曼散射效应情形下不稳定性调制的增益谱的表达式.结果表明在正常和反常两种群速度色散情形下,拉曼散射效应都会导致出现新的不稳定性区域,并且使原有的每一个谱分量的增益上升从而使谱的范围扩大.并通过分析反常色散情况下四种不同函数分布的非线性色散介质系数对不稳定性增益谱的影响,得到呈双曲函数分布的非线性色散介质最为理想.     

准二维光学系统的调制不稳定性分析

本文利用时间相关的变分法对准二维的非线性薛定谔方程平面波的调制不稳定性进行了研究。在拉格朗日变分的框架下推导出相与振幅的演化方程,进而对线性化扰动方程的解进行了数值模拟,直观地展示了平面波的调制不稳定性。最后通过对能量方程有效势的分析,严格地得到了平面波解调制不稳定的判断准则。