Numerical investigation of the fin geometry of ram accelerator projectiles in subdetonative propulsion mode

The aim of this paper is to provide data on the influence of the geometry of the fins on the acceleration performance of a ram accelerator projectile in the subdetonative mode. The data that are presented in this paper are derived from a non reacting computation performed at the French Research Institute (ISL) with the commercial numerical code TascFlow TM from AEA Technology. This code calculates the pressure and temperature profiles in a non-reactive flow around the ram accelerator projectile. Three types of projectiles were studied with respectively three, four and five fins. Furthermore, different fin geometries were studied. The wall temperature behavior was investigated, in order to explain the high erosion of the projectile that is observed as the projectile comes out of the tube. Moreover, the high temperatures that were derived from the calculation explain the initiation process of the reactive at some point of the projectile, which, in turn, explains the unstart process. These calculations were conducted during ram accelerator operations at ISL and were used to explain some effects observed on the experimental data obtained in both the 30-mm and 90-mm caliber facilities.