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Abstract
A low inductance exploding wire circuit is shown to be a good means for the investigation of variable energy cylindrical blast waves. The circuit was designed so that the energy stored in a large capacitor could be discharged with the energy transferred to the wire in a single pulse with no oscillation and no dwell time or restrike. Voltage and current can then be measured as a function of time so that energy release as a function of time can be determined.
Fine wires of silver, cadmium, and zinc were exploded in air and in argon at pressures from 150 torr to 760 torr. Energy release as a function of time was determined from measurements and schlieren photographs showing the flow field generated, taken with an ultra-high speed framing camera capable of up to 2 × 106 frames/sec. Plexiglas plates at the wire ends were employed to confine the expansion for true cylindrical symmetry.
Some comparison of the measurements was made with analyses. The measurements show that the classical blast wave theory applies reasonably well ‘long after’ the completion of the energy release. For shorter times, a characteristic time based on energy transferred and a characteristic length based on the mass of the metal vapor and the density of the ambient gas resolve some differences in shock front trajectories which result from different ambient pressures and kind of composition.
The time at which the density of metal vapor equals the density of ambient gas is shown to be about proportional to the time based on the conversion of all the energy into kinetic energy.
Methods of exploring the flow field inside the cylinder bounded by the incident shock, and of exploring inclusion of chemical reactions are also presented.