Characterization of underwater blast waves from Cu wire explosions using high-resolution pressure measurements

Blast waves resulting from underwater electrical wire explosions (UEWEs) are characterized using a high-speed camera and a hydrophone. The UEWEs are created by discharging a 10 μF pulsed power generator that delivers currents up to 170 kA to copper wires on a microsecond timescale, thereby driving their rapid phase transitions from solid to plasma. The trajectory of the resulting cylindrical blast waves is captured by a 5-Mfps high-speed camera, which forms part of a z-type shadowgraphy system. Pressure profiles of the blast waves are measured with a fiber optic hydrophone at 6, 8, and 10 mm away from the exploding copper wires of 150, 400, and 500 μm in thickness. Good agreement is found between these experimental results and simulations, which couple a zero-dimensional (0D) magnetohydrodynamic model for the wire expansion and a one-dimensional (1D) Euler model for the blast wave propagation. The simulations provide experimentally inaccessible insight into the first microseconds of the explosion, including the wire's thermodynamic and electrical properties, and the energy transfer dynamics between the wire and water. This reveals how wire diameter affects the transfer of electrical energy to the blast wave with 150 μm wires leading to underdamped electrical dynamics that generate slower blast waves and lower pressures than 400 and 500 μm wires. Overall, the experiments demonstrate blast pressures up to 500 MPa measured at 6 mm from the 500 μm wire and Mach numbers reaching 1.92 at 3 mm from the explosion center.