Numerical Simulation of the Interface Instability Inducedby Shock in Initial Nonuniform Flows
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摘要: 流体力学界面不稳定性及其后期的界面混合现象,是一种十分复杂的多尺度非线性物理问题,在惯性约束聚变、天体物理以及水中爆炸等领域有着广泛的应用前景,对该问题的研究不仅具有很高的学术价值,而且对促进相关领域的发展具有重要意义.中国工程物理研究院流体物理研究所基于Euler有限体积方法,发展了适用于可压缩多介质黏性流动具有多亚格子尺度模型的大涡模拟程序MVFT,并评估分析了不同亚格子尺度模型对界面不稳定性及界面混合的模拟能力;提出了流场非均匀性对R-M不稳定性影响的问题,并在激波驱动轻重气体双模扰动R-M界面不稳定性实验中成功应用并解读了新的实验现象和规律,在此基础上进而开展了反射激波作用下两种初始非均匀流场界面不稳定性引起的界面混合数值模拟研究,探讨了流场非均匀性对激波反射后强非线性阶段界面不稳定性发展、演化规律的影响,近期还对非均匀流场R-M不稳定性的演化规律、初始流场非均匀性和初始扰动效应及其影响的物理机制进行了分析和研究.Abstract: Interface instability and turbulent mixing are complex multi-scale nonlinear physical problems, which have been found and utilized widely in man-made applications and natural phenomena such as inertial confinement fusion(ICF), high-speed combustion, and astrophysics (i.e. supernova explosions), so this problem has gained significant attention in science and technology. The Institute of Fluids Physics, China Academy of Engineering Physics has developed a large eddy simulation code MVFT (multi-viscous flow and turbulence)with different SGS models, based on Eulerian finite volune method. Meanwhile, the ability of different SGS models for simulating the interface instability and interface mixing has been evaluated in research. The effect of nonuniformity of flow field on the Richtmyer-Meshkov (R-M) instability was put forward, which has been successfully used to explain the related new experiment phenomenon and laws of the R-M instability. Given the found mechanism, the R-M instability and interface mixing in nonuniform flow were further studied and the effect of nonuniformity on the interface instability development in the strong nonlinear stage was discussed. Recently, the effects of initial perturbation on the R-M instability have been researched as well. Distinctive evolution mechanisms of R-M instability between the nonuniform flows and the uniform flows were analyzed in detail.
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图 15 大小扰动振幅历程的理论、实验与数值计算结果比较(其中误差棒为实验值的10%)
Figure 15. Perturbation amplitudes history of experiment, numerical computing and comparison to Sadot model and Zhang-Sohn theory, B1-S1 corresponds to small perturbation amplitude, and B3-S3 corresponds to large one (error bars of this visual measurement are equal to ±10%)
图 18 t=1 ms不同初始振幅组合下的流场密度云图(左列:低密度均匀流场; 中列:高密度均匀流场; 右列:非均匀流场)
Figure 18. Density contour images of numerical simulation results at t=1 ms under different groups of initial amplitudes (left column shows low-density uniform flows; middle column high-density uniform flows; and right columnnonuniform Gaussian function flows)
图 19 t=1.8 ms不同初始振幅组合下的流场密度云图(左列:低密度均匀流场; 中列:高密度均匀流场; 右列:非均匀流场)
Figure 19. Density contour images of numerical simulation result at t=1.8 ms under different groups of initial amplitudes (left column shows low density uniform flows; middle column high-density uniform flows; and right column nonuniform Gaussian function flows)
图 23 t=1 ms, 不同初始扰动振幅下, 非均匀流场高密度区S3、低密度区S1、均匀流场高低密度区, 波谷处的涡量平均值分布图
Figure 23. Average vorticities of four conditions: the spike trough in low-density zone of nonuniform flows S3, the spike trough in high-density zone of nonuniform flows S1, and the spike trough in low-density uniform flows and high-density uniform flows with four initial amplitudes at t=1 ms
图 25 初始振幅为(a)7.5 mm情况下, 非均匀流场高低密度区、高低密度均匀流场区, 4/3波长面积内总环量、正环量、负环量时间图; 初始扰动振幅分别为: (b)2.5 mm, (c)5 mm, (d)7.5 mm, (e)10 mm情况下, 非均匀流场高低密度区、高低密度均匀流场区, 4/3波长面积内负环量时间图
Figure 25. Circulations over time in four conditions: low-density zone of nonuniform flows, high-density zone of nonuniform flows, low-density uniform flows, and high-density uniform flowsunder four initial amplitudes
图 26 密度云图和涡量云图(左列:均匀流场, 中列: δ1 Gauss分布的非均匀流场, 右列: δ2 Gauss分布的非均匀流场)
Figure 26. Density and vortex contour images of the numerical simulation results by MVFT at certain times (Left column, uniform initial conditions; middle column, δ1 nonuniform Gaussian function; and right column, δ2 nonuniform Gaussian function. Small arrow denotes the direction of propagation of the shock wave fronts before reshock of the interface)
表 1 激波再加载前后不同SGS模型计算时湍动能衰减常数
Table 1. Decay constants of turbulent kinetic energies before and after reshock for different SGS models
models VM DSM SVM before reshock 0.076 99 0.100 78 0.083 18 after reshock 0.087 62 0.049 7 0.075 48 表 2 空气和SF6的物理参数
Table 2. Properties of air and SF6 gases
gases densities (g/cm3) specific ratios kinetic viscosities (10-6m2/s) Prandtl numbers diffusion coefficients in air (cm2/s) air 1.29 1.40 15.7 0.71 0.204 SF6 5.97 1.09 2.47 0.90 0.097 表 3 振幅组合表
Table 3. Six groups of initial amplitudes
No. A01/mm A02/mm 1 5 7.5 2 7.5 5 3 2.5 7.5 4 7.5 2.5 5 5 10 6 10 5 表 4 t=1 ms时, 初始振幅为2.5, 5, 7.5, 10 mm情况下, 均匀流场高低密度区、非均匀流场高低密度区4/3波长面积内环量对比表
Table 4. Negative circulations of five initial amplitudes in four flow field at t=1 ms
A0/mm Γ- in low-density of uniform flows /(m2·s-1) Γ- in high-density of uniform flows /(m2·s-1) Γ- in high-density of nonuniform flows /(m2·s-1) Γ- in low-density of nonuniform flows /(m2·s-1) 2.5 -1.02 -1.96 -2.94 -5.01 5 -2.72 -3.43 -4.93 -6.55 7.5 -5.37 -6.53 -7.07 -8.81 10 -6.91 -8.79 -9.23 -11.40 0.0 0.00 0.00 -0.35 -3.42 -
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