Explosive Modeling: Airblast Anatomy | Pete and RePete

One interesting feature of detonation and airblast propagation is the formation of a second shock wave propagating from the origin of the detonation. The primary shock is sometimes referred to as “Pete” with the second shock, that reflects from the center of the charge, called “RePete”. RePete shock will form in any symmetrically detonated solid explosive but is strongest in a spherical or surface flush hemispherical charge. RePete is readily observed using high speed photography as a brightening inside the detonation products caused by shock heating as the reflected shock progresses. To illustrate this phenomenon, consider an axis-symmetric blastFoam simulation of a 1m radius surface flush hemispherical charge (approximately 3,400 kg TNT). The charge is center detonated and when the detonation wave reaches the surface of the charge, the air immediately outside the charge is rapidly accelerated and a rapid expansion occurs. After 3.0 msec the shock front has expanded to ~10 times the initial charge radius.