The Growth of Richtmyer-Meshkov Instability under Multiple Impingements

The growth of multi-mode Richtmyer-Meshkov instability under multiple impingements and the effect of initial shock strength on the growth of RMI are numerically investigated. We obtain the time evolution of turbulent mixing zone width for initial shock with different strength. The results show that the turbulent mixing zone width grows in a different manner at different stage but strictly in a similar way for the initial shock with different strength. Also, the initial shock strength has a significant effect on the growth rate of turbulent mixing zone width, especially before reshock, but can not change the growth laws in the whole process.

Large-Eddy Simulation of the Three-Dimensional Experiment on Richtmyer-Meshkov Instability Induced Turbulence

A program MVFT3D of large-eddy simulation is developed and performed to solve the multi compressible Navier- Stokes equations. The SGS dissipation and molecular viscosity dissipation have been analyzed, and the former is much larger than the later. Our test shows that the SGS dissipation of Vreman model is smaller than the Smagorinsky model. We mainly simulate the experiment of fluid instability of shock-accelerated interface by Poggi in this paper. The decay of the turbulent kinetic energy before the first reflected shock wave–mixing zone interaction and its strong enhancement by re-shocks are presented in our numerical simulations. The computational mixing zone width under double re-shock agreement well with the experiment, and the decaying law of the turbulent kinetic energy is consistent with Mohamed and Larue’s investigation. Also, by using MVFT3D we give some simulation results of the inverse Chevron model from AWE. The numerical simulations presented in this paper allow us to characterize and better understand the Richtmyer-Meshkov instability induced turbulence, and the code MVFT3D is validated.

Computational Analysis of the Metal Free-Surface Instability, Fragmentation, and Ejecta under Shock

We conducted numerical simulations of the related processes of interface instability, tensile fragmentation, and jetting resulting from four kinds of typical macro defect perturbations (chevron, sine wave, rectangle, and square) on a Cu free surface under a reflected shock wave when Cu impacts a solid wall at a speed of 2.5 km/s and found that, for the chevron and sine wave cases, the ejecta velocities of the head are 6.28 and 5.88 km/s, respectively. Some parts of the inner material are in a tensile state without any fragmentation, which is observed only in the main body of the material owing to the tension effect. Furthermore, for the other two initial perturbations (rectangle and square), the highest ejecta velocities may even reach 9.14 and 9.59 km/s, respectively. Fragmentation caused by multilayer spallation can be observed on a large scale in the Cu main body, and there are granules in the front area of the ejecta but the degree to which fragmentation occurs is much less in the Cu main body and there is a notable high-speed, low-density granule area in the ejecta head. Finally, we present a detailed analysis of the spatial distribution of the granules, ejecta mass, pressure, temperature, and grid convergence.

Numerical Investigation of Bismuth Unloading Solidification with Abnormal Melting Characteristic

We present the processes and results of a numerical investigation of the bismuth unloading solidification by a graded density impactor, and demonstrate that the physical process may be realized due to bismuth abnormal melting characteristics. A more reasonable high-pressure solid equation of state of the fifth phase bismuth is introduced in our calculation and one type of graded density impactor made of 15 compositions of Mg-Cu material system is given in this paper. We detailedly investigate one possible proposed approach to achieve the unloading solidification physical process, and our numerical analysis on the thermodynamic state, the unloading path and the phase transformations.

Evolution of Hydrodynamic Instability on Planar Jelly Interface Driven by Explosion

A high precision numerical algorithm MVPPM (multi-viscous-fluid piecewise parabolic method) is proposed and applied to study the multi-viscous-fluid dynamics problems. Three planar jelly experiments with periodic cosine perturbation on the initial interface have been conducted and numerically simulated by MVPPM. Good agreement between experimental and numerical results has been achieved, including the shape of jelly interface, the displacements of front face of jelly layer, bubble top and spike head. The effects of initial conditions (including amplitude and wave length of perturbation, thickness of jelly layer, etc.) on the evolution of the jelly interface have been numerically analyzed. It is found that the key affecting factors are the perturbation amplitude and thickness of jelly layer. The hydrodynamic instability on double planar jelly layers driven by explosion has been investigated numerically to examine their laws of evolution, and an interesting phenomenon is observed.