Based on multi-fluid volume fraction and piecewise parabolic method(PPM),a multi-viscosity-fluid hydrodynamic code MVPPM(Multi-Viscosity-Fluid Piecewise Parabolic Method) is developed and applied to the problems of shock-induced hydrodynamic interfacial instability and mixing.Simulations of gas/liquid interface instability show that the influences of initial perturbations on the fluid mixing zone(FMZ) growth are significant,especially at the late stages,while grids have only a slight effect on the FMZ width,when the interface is impulsively accelerated by a shock wave passing through it.A numerical study of the hydrodynamic interfacial instability and mixing of gaseous flows impacted by re-shocks is presented.It reveals that the numerical results are in good agreement with the experimental results and the mixing growth rate strongly depends on initial conditions.Ultimately,the jelly layer experiment relevant to the instability impacted by exploding is simulated.The shape of jelly interface,position of front face of jelly layer,crest and trough of perturbation versus time are given;their simulated results are in good agreement with experimental results.
Based on the numerical methods of volume of fluid (VOF) and piecewise parabolic method (PPM) and parallel circumstance of Message Passing Interface (MPI),a parallel multi-viscosity-fluid hydrodynamic code MVPPM (Multi-Viscosity-Fluid Piecewise Parabolic Method) is developed and performed to study the hydrodynamic instability and flow mixing. Firstly,the MVPPM code is verified and validated by simulating three instability cases:The first one is a Riemann problem of viscous flow on the shock tube; the second one is the hydrodynamic instability and mixing of gaseous flows under re-shocks; the third one is a half height experiment of interfacial instability,which is conducted on the AWE's shock tube. By comparing the numerical results with experimental data,good agreement is achieved. Then the MVPPM code is applied to simulate the two cases of the interfacial instabilities of jelly models acceler-ated by explosion products of a gaseous explosive mixture (GEM),which are adopted in our experi-ments. The first is implosive dynamic interfacial instability of cylindrical symmetry and mixing. The evolving process of inner and outer interfaces,and the late distribution of mixing mass caused by Rayleigh-Taylor (RT) instability in the center of different radius are given. The second is jelly layer ex-periment which is initialized with one periodic perturbation with different amplitude and wave length. It reveals the complex processes of evolution of interface,and presents the displacement of front face of jelly layer,bubble head and top of spike relative to initial equilibrium position vs. time. The numerical results are in excellent agreement with that experimental images,and show that the amplitude of initial perturbations affects the evolvement of fluid mixing zone (FMZ) growth rate extremely,especially at late times.
The Navier-Stokes equations for compressible fluid are solved with the operator splitting technique and LES (large eddy simulation) with the Smagorinsky model. A computational code MVFT (multi-viscosity-fluid and turbulence) is developed to study hydrodynamic instability and the induced turbulent mixing for multi compressible fluid. In order to validate the code MVFT,the LANL's shock tube experiment of shocked SF6 gas cylinder is simulated with the initial state of SF6 gas cylinder described by dissipative ITL (interface transition layer). It is shown that the width and height of gas cylinder calculated with MVFT are closer to the experimental results than RAGE,and that the velocities of upstream edge,downstream edge and vortex edge agree with the experimental results,and are appreciably smaller than the RAGE results. The code MVFT has been pre-liminarily validated.
LI Ping,BAI JingSong,WANG Tao & ZOU LiYong National Key Laboratory for Shock Wave and Detonation Physics Research,Institute of Fluid Physics,CAEP,Mianyang 621900,China
在可压缩多介质粘性流体动力学高精度计算方法MVPPM(multi-viscous-fluid piecewise parabolicmethod)基础上,引入Smagorinsky和Vreman亚格子湍流模型,采用大涡数值模拟方法求解可压缩粘性流体NS(Navier-Stokes)方程,给出适用于可压缩多介质流体界面不稳定性发展演化至湍流阶段的计算方法和二维计算程序MVFT(multi-viscosity-fluid and turbulence)。在2种亚格子湍流模型下计算了LANL(Los Ala-mos National Laboratory)激波管单气柱RM不稳定性实验,分析了气柱的形状、流场速度以及涡的特征,通过与LANL实验和计算结果的比较可知,Vreman模型略优于Smagorinsky模型,MVFT方法和计算程序可用于对界面不稳定性发展演化至湍流阶段的数值模拟。
利用CE/SE(conservation element and solution element)格式研究了柱面会聚波在气体中传播时间断面的不稳定问题和波阵面的演变问题,并利用level set函数追踪了驱动气体与低压气体间断面的发展过程。得到了间断面的Rayleigh-Taylor(R-T)和Richt myer-Meshkov(R-M)不稳定性发展成典型的"尖钉"和"气泡"结构的图像,初始正弦扰动下的会聚波产生"尖角"和"尖瓣"结构。结果表明,CE/SE格式在涉及会聚波的数值计算中是可行的。
