Analysis of Hydrodynamic Lubrication Considering the Self-Acceleration of a Liquid Conducting Film at Rail–Armature Interface

Abstract

In a railgun, the melting of the armature as a result of great frictional and Joule heating forms a liquid conducting film over the rail–armature contact surfaces. The magnetic field was concentrated in the trailing surface of the armature and liquid film due to the velocity skin effect. Electromagnetic forces in the longitudinal direction acting on the armature and liquid film could cause a self-acceleration in the film. However, the magnetic lateral force in the film squeezes the armature legs against the rails in the transverse direction. Thus, a diverging film, with a minimum thickness at the leading edge, forms at the rail–armature interface due to easier tail deformation than head for traditional C-shaped armature legs. This paper attempts to investigate the effect of self-acceleration in this diverging film on hydrodynamic lubrication and compared with the traditional lubrication model. Total pressure distribution considering uniform and nonuniform film accelerations is investigated, respectively. It is found that the film’s self-acceleration can generate the positive pressure, strengthening the total pressure distribution. Furthermore, conditions for generating positive pressure distribution under different film accelerations are analyzed and discussed. The results show that the film acceleration can decrease the minimum film’s slope that produces a positive pressure distribution. Total pressure distribution can maintain positive at thinner film when the film acceleration is considered.