Stability Analysis of Hydrodynamic Lubrication of a Liquid Conducting Film at Rail–Armature Interface

The liquid conducting film flowing along a diverging gap between rail and armature in a railgun is considered. This paper attempts to investigate whether the liquid film flowing along a diverging gap can achieve purely hydrodynamic lubrication preventing direct contact between rail and armature. Specific cases of linearly diverging gaps are assumed with a minimum thickness at leading edge. Analytical solution of pressure distribution is obtained with the lubrication approximation. The carrying capability of film is estimated by integrating the pressure distribution numerically. Conditions for stable liquid film are proposed through analyzing positive pressure distribution and carrying capability of the film. If the film can generate positive pressure distribution and its carrying capability is able to support the contact force between rail and armature, stable film appears which can prevent direct contact between the rail and armature surfaces achieving purely hydrodynamic lubrication. In the end, hydrodynamic lubrication stability of a liquid conducting film under different film thickness and launching mass are analyzed and discussed. It is found that the film's stability can be improved with the increase of film thickness and launching mass. A thicker film and heavier load are well expected in order to realize hydrodynamic lubrication at high speed.