Pulsation Dynamics of Explosively Formed Channel Jets

Explosively formed channel jetting is a widely known effect, though the physical understanding of its formation is less well understood. For long enough channels, such jets are seen to pulsate in periodic fashion under the optimal geometric driving conditions for a given explosive. The mechanics of these pulsations are interesting and perhaps even less well understood. A series of jetting experiments were conducted within planar air channels formed between adjacent slabs of PBX 9501. Previous experiments in the series have shown that jetting damage to an incident material at the end of the channel peaks at an optimal non-zero channel width. The pulsations within these channels are present at each varying width but appear to change in character as a function of this geometry. Streak camera tracking of the pulsation reveals that the oscillation at the leading jet front is not a solitary shock fluctuating in speed, but the result of successive jets that individually push ahead before losing speed and energy, each being overtaken by a trailing pulse as the cycle repeats. The physical mechanism for such behavior is discussed and analyzed.