3-D plasma armature railgun simulations

A three-dimensional Navier-Stokes code has been extended to provide a simulation for the railgun plasma armature. This code was previously used with an approximate electromagnetic model to provide a two-dimensional simulation of a railgun plasma armature flow in the plane containing the insulators. A new three-dimensional electromagnetic solver has been incorporated into the code to permit full 3-D nonsteady MHD simulations of the plasma armature flow in a railgun. The finite-difference equations for magnetic vector potential and electric potential are solved using the ICCG method. The new electromagnetic solver was validated using 3-D solutions obtained from the finite element electromagnetic code MEGA. A full bore, 3-D simulation of a plasma armature reveals flow patterns significantly different than those of rail or insulator plane 2-D simulations. In particular, the maximum J/spl times/B force occurs off-axis and results in a plasma flow away from the projectile along the axis of symmetry. A zone of high shear flow forms near the rail surfaces which increases the viscous losses. Zones of low current, nearly stagnant flow form near the base of the projectile, consistent with experimental observations of a buffer between the armature and the projectile.<>