Dynamics of explosively imploded pressurized tubes

Abstract

The detonation of an explosive layer surrounding a pressurized thin-walled tube causes the formation of a virtual piston that drives a precursor shock wave ahead of the detonation, generating very high temperatures and pressures in the gas contained within the tube. Such a device can be used as the driver for a high energy density shock tube or hypervelocity gas gun. The dynamics of the precursor shock wave were investigated for different tube sizes and initial fill pressures. Shock velocity and standoff distance were found to decrease with increasing fill pressure, mainly due to radial expansion of the tube. Adding a tamper can reduce this effect, but may increase jetting. A simple analytical model based on acoustic wave interactions was developed to calculate pump tube expansion and the resulting effect on the shock velocity and standoff distance. Results from this model agree quite well with experimental data. V

Implosion-driven technique to create fast shockwaves in high-density gas

“…A simple model of the dynamics of the radial expansion of the pressurized tube and its interaction with the surrounding (liquid) explosive and tamper has been developed that uses acoustic wave tracking [1]. This model is justified since the radial motion of the tube (order of 100 m/s) is much less than the sound speed of the explosive (1500 m/s) into which it expands.…”

“…As such, we can express the total pressure as the instantaneous change in pressure felt by a differential segment of wall summed with the reflected pressure. This algorithm is described in detail by Szirti [1], and is used iteratively in the case of a three-body problem. Should an intermediate tamper exist between the pressurized tube and the outer tamper, the same algorithm may be applied at each time step.…”

“…The experiment test set-up was based on that of Szirti et al [1], with the design modified to permit an intermediate layer of metal of various thicknesses to be inserted into the explosive layer. The schematic of a typical charge is shown in Figure 5.…”

“…In addition to applications of high energy density physics, such devices can also be used as drivers for hypervelocity launchers. A recent study of the dynamics of implosion-driven shock waves and interaction with the resulting radial expansion of the tube identified the use of a thick-walled tamper surrounding the explosive as integral to effective operation of the device [1]. In addition to providing confinement of the detonation products and focusing more energy release inward to implode the tube, the tamper also plays an essential role in helping confine the dynamic expansion of the tube due to the gas shock, delaying rupture of the tube prior to the arrival of the detonation.…”

Phase velocity enhancement of linear explosive shock tubes

“…In the ideal case where the tube pinch acts as an impermeable piston and the tube walls are rigid until implosion, the shock wave continuously moves ahead of the pinch with a velocity determined by the following equation [4]: where U p is the virtual piston or pinch velocity, c 0 is the initial sound speed of the gas, γ is the ratio of specific heats of the gas and M s is the Mach number of the shock.…”