546 / 2019-03-20 12:02:04

Multiscale numerical simulations on Richtmyer-Meshkov instability under extreme conditions

Richtmyer-Meshkov instability; extreme conditions; similarity; multiscale; simulations;

全体主题 > Interface Instabilities at Extremes

The Richtmyer-Meshkov instability (RMI) phenomenon under extreme impacting conditions is one of key and basic topic in the field of inertial confinement fusion (ICF). It is most challengeable due to extreme shock compressing conditions (high energy density environment: P >> 100GPa, T >> 10000k). The evolution may be full of scientific problems and academic interests. However, due to the lack of proper models in extreme conditions, macroscopic hydrodynamic methods and experiments are difficult to learn the basic mechanism in such states, while the molecular dynamics (MD) simulations are effective for mechanism analysis in microscopic views but difficult be directly applied in macroscopic scales due to computational costs. Therefore, it is of great significance to conduct multiscale simulations on RMI problems under extreme conditions.
In present investigation, it is found that all RMI amplitude evolution curves behave with self-similarity under similar dynamic conditions and boundary conditions, all main parameters vary in accordance with prediction of theoretical model based on comprehensive multiscale RMI simulations and models analysis. The connection between macroscopic and microscopic RMI are preliminarily established. Then a strong acceleration of metal/gas interface after strong shock compression was observed numerically in MD simulations. It is recognized as a new mechanism induced by the extra electric field of the electron/ion separation under extreme shock compression states. Further multiscale studies reveal that the electron/ion separation is moving with shock. Its intensity and width of electron/ion separation zone are kept to be constant approximatively during shock propagating process and determined by shock strength. An analytical extra acceleration evaluation model of Li/H2 interface under impacting velocity range of 20~80km/s are established. To further bridge the microscopic process to macroscopic behavior in RMI under extreme conditions, a numerical multiscale code based on particle dynamics such as MD, SPH, etc. is proposed. Preliminary validation simulations prove its effectiveness and reliabilities in distinguish and track strong shock waves and strong interface discontinuities. The related algorithms development lays solid foundation for future multiscale simulations.