A thermal hydraulic model of melt-lubrication in railgun armatures

This paper describes the first step toward a model of the liquid film at th e rail-armature interface in solid armature railguns, The model considers h igh-speed Couette flow with viscous treating. It does not include magnetohy drodynamic body forces or Joule heating. The focus of the model is on coupl ed fluid dynamics and multiphase heat transfer. The formulation is similar to the analysis of melt lubrication in rotating projectile bands, However, our first principles model allows the possibility of solidification while t he armature is passing, a feature that has been missing from previous analy zes. The model is moderately successful at reproducing results of experimen ts that measured high-speed mechanical wear of 7075 aluminum sliding agains t electrolytic tough pitch (ETP) copper for face pressures ranging from 45 to 150 MPa. Discrepancies between calculated and experimental results are d iscussed. Possible causes include 1) inadequacy of the laminar flow approxi mation, 2) uncertainties in modeling the complex phase change behavior of a luminum alloy 7075, and 3) thermal contact resistance at the rail interface .