An experimental and numerical study of weak spherical N-waves produced by exploding wires

The effects of vibrational excitation of oxygen molecules on the transition shape and thickness of shocks in weak, spherical N-waves produced in air by exploding tungsten wires was investigated experimentally and numerically. Extensive measurements were made in a still-air dome of the overpressure signatures of N-waves at distances ranging from 15 to 150 ft (4.6 to 45.7 m) from the exploding wires, over which the amplitude of the front shock decayed from 250 to 5 Pa and the positive-phase duration increased from 70 to 150 micro-sec. The amplitudes and rise times of both the front and near shocks, as well as the durations of the positive and negative phases, were taken from the measured N-wave signatures, tabulated and plotted. The experimental data were then compared to predicted results from a numerical simulation, by using the explosion of a pressurized air sphere as a model. The explosion flow field containing the outward moving spherical N-wave was computed by employing the random-choice method with an operator-splitting technique to solve the full Navier-Stokes equations, including the vibrational excitation of oxygen molecules. The experimental and numerical results are in fair agreement, and additional numerical work is recommended.