  The generation of plasma from hypervelocity impacts is an active research
topic due to its important science and engineering ramifications in various
applications. Previous studies have mainly focused on the ionization of the
solid materials that constitute the projectile and the target. In this letter,
we consider impact events that occur in a fluid (e.g.,~gas) medium, and present
a multiphysics computational modeling approach and associated analysis to
predict the behavior of the dynamic fluid-solid interaction that causes the
surrounding fluid to ionize. The proposed computational framework is applied to
a specific case involving a system of three interacting domains: a copper rod
projectile impacting onto a soda lime glass target in a neon gas environment.
The impact velocity is varied between 3 km/s and 6 km/s in different
simulations. The computational model couples the compressible inviscid
Navier-Stokes equations with the Saha ionization equations. The three material
interfaces formed among the projectile, the target, and the ambient gas are
tracked implicitly by solving two level set equations that share the same
velocity field. The mass, momentum, and energy fluxes across the interfaces are
computed using the FInite Volume method with Exact two-material Riemann
problems (FIVER). The simulation result reveals a region of neon gas with high
velocity, temperature, pressure, and mass density, formed in the early stage of
the impact mainly due to the hypersonic compression of the fluid between the
projectile and the target. For impact velocities higher than 4 km/s, ionization
is predicted in this region.
