Shock-turbulence Interaction and Richtmyer-Meshkov Instability in Spherical Geometry

Book excerpt: The canonical problems of shock-turbulence interaction and Richtmyer-Meshkov instability (RMI) are central to understanding the hydrodynamic processes involved in Inertial Confinement Fusion (ICF). Over the last few decades, there has been considerable analytical, computational and experimental work on the planar versions of these problems. In spite of the problem of interest being spherical in nature, there have been few studies in any of the three areas for these problems. It is not clear a priori, that the conclusions drawn from planar versions of these problems carry over to the spherical domain. The research presented here represents a first attempt to understand the hydrodynamic processes involved in an Inertial Fusion Engine (IFE) from capsule implosion to interaction of the resulting shock waves with the chamber gases. To abstract the key hydrodynamic components from the complex physics involved in an IFE, three canonical problems are identified and simulated: Interaction of a blast wave with isotropic turbulence, interaction of a converging shock with isotropic turbulence and RMI in spherical geometry. The last problem is a hydrodynamic abstraction of the capsule implosion itself, while the first two problems attempt to model the late stage interaction of fusion induced shock waves with chamber gases. On the shock-turbulence front, the study primarily focuses on the effect of shock strength relative to background turbulence on vorticity dynamics, which forms the cornerstone of any turbulence simulation. The effect of turbulence on shock structure is also characterized. For the converging shock, the maximum compression achieved in presence of turbulence is compared with that for a pure shock. For spherical RMI, focus is on evolution of the mixing layer and growth in vorticity and turbulent kinetic energy for different incident shock Mach numbers. The effect of interface perturbation on maximum compression achieved, which is one of the most important metrics for feasible ICF, is also considered.