A thermal hydraulic model of melt-lubrication in railgun armatures

This paper describes the first step toward a model of the liquid film at the rail-armature interface in solid armature railguns. The model considers high-speed Couette flow with viscous heating. It does not include magnetohydrodynamic body forces or Joule heating. The focus of the model is on coupled fluid dynamics and multiphase heat transfer. The formulation is similar to the analysis of melt lubrication in rotating projectile bands. However, the authors' first principles model allows the possibility of solidification while the armature is passing, a feature that has been missing from previous analyzes. The model is moderately successful at reproducing results of experiments that measured high-speed mechanical wear of 7075 aluminum sliding against electrolytic tough pitch (ETP) copper for face pressures ranging from 45 to 150 MPa. Discrepancies between calculated and experimental results are discussed. Possible causes include: (1) inadequacy of the laminar flow approximation; (2) uncertainties in modeling the complex phase change behavior of aluminum alloy 7075; and (3) thermal contact resistance at the rail interface.