Experimental analysis of 7.62 mm hydrodynamic ram in containers

The design of fuel tanks with a reduced vulnerability with respect to hydrodynamic ram pressure (HRAM) effects is of an increasing need in the Civil (e.g. the Concorde accident), and Defence (military aircraft, unmanned vehicle systems) aircraft industries. The presented work concerns experimental research which aims at observing two hydraulic ram events – both induced by a 7.62 mm bullet shot in very different containers – throughout their various steps until the final collapse of the generated cavity, in order to study the nature of HRAM, the influence of the containers geometry, and to measure original dynamic data for numerical modelling developments and validation. For that purpose, test configurations and experimental results are described, documented and discussed. They concern two types of firing tests that were performed at ONERA using the NATO 7.62 mm projectile, respectively in the frame of ONERA (pool) and EUCLID (caisson) funded research projects. The authors concentrate on two topics: on the one hand, digital image analysis to measure the cavity geometry during its growth and collapse phases and, on the other hand, pressure measurements that catch the transient shock wave. The originality of the work consists in the fact that – compared with other published works – the phenomenon is studied up to tens of milliseconds in a very large pool for theoretical analysis of the bullet/liquid interactions only, and in a realistic fuel tank specimen to consider influence of boundary conditions onto the cavity characteristics (geometry, dynamics).