极端条件下材料混合的分子动力学研究

Understanding of material mixing induced by Richtmyer-Meshkov instability (RM instability) in extreme conditions （high energy environment：P>>100GPa,T>>10000k） is of great significance in engineering and science, such as ICF(inertial confinement fusion), supersonic combustion, etc, . Turbulent mixing induced by RM instability is a kind of complex fluid dynamics, which is closely related with hydrodynamic conditions /thermodynamic states, material physical properties such as compressibility, strength, surface tension, viscosity etc. , and initial perturbation on interface. For phenomena in ordinary thermodynamic conditions (low energy environment), many investigations have been conducted and many progresses have been reported, while for mixing in extreme thermodynamic conditions, the evolution may be very different due to ionization as well as large difference of material physical properties, which is full of scientific problems and academic interests. Literature review reveals that the related investigations are rightly started and filled with challenges. In this proposal, material properties in extreme conditions are firstly calculated with first principle molecular dynamics (FPMD), and interaction potentials of different materials (Pb and He) under different extreme conditions will be developed. Then material mixing cases with different thermodynamic conditions will be computed with large-scale molecular dynamics based on new developed potentials and some validation experiments will be conducted. Finally, the difference of basic evolution features and physical mechanism in metal/gas mixing induced by RM instability between ordinary thermodynamic state and extreme thermodynamic state will be carefully investigated.

研究极端条件下（高能量环境：压力>>百GPa，温度>>万开）由RM不稳定性诱发的材料混合在惯性约束聚变（ICF）、超音速燃烧等领域具有重大的工程意义和学术价值。由RM不稳定性诱发的湍流混合，是一种与动力学条件-热力学状态、材料物性（可压缩性、强度、表面张力、粘性等）、界面初始扰动等三方面因素密切相关的复杂流体动力学现象。对于一般热动力学状态下（低能量环境）的此类现象，国内外已开展有较多实验与数值模拟研究。极端热动力学状态下，物质将发生电离，材料物性将发生较大变化，混合行为预期也将与非极端条件有较大变化，相关问题研究国内外目前均处于起步阶段。本研究利用第一性原理分子动力学方法，获得极端条件下的材料物性并发展相关势函数，进而开展不同热动力学条件下铅、氦材料混合的分子动力学数值模拟，并结合实验，揭示极端条件与非极端热力学条件下金属/气体RM不稳定性诱发湍流混合物理机制及其差异。

冲击加载下的材料混合界面不稳定性是目前惯性约束核聚变研究中的关键基础问题，其挑战主要来源于极端热动力学条件（P≫100GPa,T ≫10000 K），特别是物质电离引起的材料物性、热力学状态等性质的急剧变化，为相关理论、实验和数值模拟带来巨大的挑战。本研究针对极端条件下的材料混合问题，开展了基于分子动力学的微观模拟及宏观实验,主要进展包括：（1）验证了微纳米尺度下的RMI 同宏观尺度下的RMI 有相似的演化现象，在计算时间尺度内满足相同演化规律，为宏观实验与微观模拟结果的比较与验证提供了理论依据；（2）发现极端加载条件下RMI 的演化呈现新的特征，即振幅增长的线性段加长和非线性段振幅增长速度高于无电离效应算例，并得到了Nova 实验结果证实及本研究宏观实验结果的印证；这一结果为首次发现。（3）发现极端条件下，激波作用会产生电荷分离，并诱导附加电场产生。获得了附加电场对运动界面的加速模型及影响机理，为相关新现象提供了物理解释；（4）发现极端加载的柱面汇聚过程中，汇聚激波诱导的电荷分离效应会对汇聚过程和汇聚点产生重要影响；（5）发展了一种基于SPH接触算法的界面高保真新算法,获得了清晰的多介质大密度差界面演化模拟结果，为发展界面多尺度模拟奠定了算法基础。总之，本研究结合理论模拟和实验，建立了从微观到宏观的研究技术途径，获得了从非极端到极端加载压力范围内界面扰动演化规律的新认识，并且取得了精细的理论模拟结果和实验数据，为进一步开展理论建模和数值模拟奠定了基础