Vorticity Dynamics in Hydrodynamic Simulations of Shocked Metals

When a shock wave passes through the interface between two fluids of different densities, the  Richtmyer–Meshkov instability (RMI) forms. It is well known that the baroclinic term of the vorticity equation is the driving mechanism of RMI. The baroclinic term is nonzero when the cross product of pressure and density gradients at the interface is nonzero. When a shock passes through an interface with defects, the subsequent baroclinic acceleration evolves into jets of outflow mass. The amount of outflow mass depends on the initial defect shape and size.

We use Los Alamos National Laboratory's FLAG hydrodynamics code to simulate the evolution of interfaces between gaseous helium and a tin plate with various defect shapes. The initially solid tin is fully liquid after it is subjected to a 28 GPa shock. We calculate the components of the vorticity budget, including baroclinicity, along the surface of the defect. This allows us to investigate the effect of each term in the vorticity equation on the resulting jet and to gain mechanistic insights into the variability of outflow mass from different defect shapes.