Modeling of RF plasma kinetics and aerodynamics of the AEDC ballistic range experiments

We have performed a computational study of the experiments performed by Lowry et al.^1,2 at the Arnold Engineering Development Center (AEDC). In these experiments, a RF discharge is used to weakly ionize a volume of air; then a projectile is fired through this plasma. Relative to the conditions without the discharge, the shock standoff distance is observed to increase substantially, and the bow shock becomes flatter. We have modeled the RF discharge and the resulting thermo-chemical state of the air within the discharge region. Based on these conditions, the projectile flow field was simulated to determine if the relaxation of the stored internal energy causes the observed shock movement. The results obtained to date indicate that the stored internal energy does not relax fast enough to reproduce the experimental results, and therefore vibrational energy storage is not responsible for the observed shock movement. We consider two additional mechanisms to explain the experiments: modification of the electric field by the presence of the metallic projectile, and non-uniformities in the plasma. The latter effect appears to be the leading candidate.