A moving projectile in the intermediate ballistic regime experiences several complicated flow interactions. This includes the projectile interaction with an unsteady jet into which the former is discharged from the barrel. The instantaneous loads acting on the projectile varies tremendously as it first encounters the expansion fan emanating from the launch tube exit and later passes through the shock cell or the Mach disk as a part of the unsteady jet-projectile interaction. This leads to another phenomenon called as the unsteady shock diffraction in this study, where the moving body pierces through a standing shock (the Mach stem). Even though the varying forces due to the interactions result in a substantial instantaneous acceleration or deceleration of the projectile, the entire phenomenon happens within a very small timescale of milliseconds. Therefore the resultant changes in velocity of the projectile during these flow interactions are negligible. The projectile’s relative velocity continues to vary as it proceeds through the jet and finally overtakes the contact discontinuity, further changing the relative velocity to a value corresponding to the post-primary blast flow. There can be an oblique shock or a detached bow shock associated with the projectile depending on its geometry and the relative Mach number. Further, the projectile interacts with the primary blast wave, categorized as a shock-shock interaction in a supersonic projectile and is known as the projectile overtaking phenomenon. The blast overtaking phenomena result in iii favourable pressure gradient on the projectile, where a low-pressure region is acting at the front face of the projectile and a high-pressure region at the rear end. This interaction becomes significant if the overtaking happens at the immediate vicinity of the launch tube exit, with a less attenuated strong primary blast wave. Once the projectile completely overtakes the primary blast wave, it enters to the external ballistic regime.

In this study, the flow interactions of a moving projectile in the intermediate ballistic regime are explored experimentally with time-resolved optical flow visualization techniques. Further, it is extended to numerical and analytical modelling for the extraction of quantitative data.