Comparison Study on Underwater Bubble Dynamics via Pulsed Discharge and Electrical Explosion

The electrohydraulic discharge is an effective and safe method to carry out laboratory simulations of underwater explosion effects. This work made a detailed comparison study on electrical and fluid characteristics of underwater pulsed discharge (UPD) and underwater electrical wire explosion (UEWE). High-speed photography synchronized with optical-electrophysical diagnostics has been applied to understand the multi-physical process. The results exhibit obvious differences between the two approaches. Under 6.4 J stored energy, the energy deposited into UEWE load can reach 3.34 J (eta > 50%), which is 2.4 times higher than that of UPD. The electric power peak is similar to 14.69 MW for UEWE, while similar to 500 kW for UPD. Under atmospheric pressure, the diameter of UEWE bubble of its 1st pulsation can reach 25.6 mm, while UPD is only 19.5 mm. Accordingly, the expansion rate of UEWE bubble can reach 51 m/s (UPD of 42 m/s). Further increase the stored energy to 12.1 J, the maximal size of UEWE bubble reaches 31 mm (potential energy 1.56 J). Morphologically, the UPD bubble is initially irregular, determined by the pre-developed streamer, whereas UEWE exhibits typical cylindrical-spherical evolution process. In later stage of bubble evolution (collapse and 2nd pulsation), the UPD bubble remains regular, whereas UEWE bubble appear irregular shape with spikes. When elevate or increase the ambient pressure, the maximal radius of the bubble decreases or increases accordingly. Particularly, the shock waves of the whole oscillation of UEWE bubble are detected in the sound-absorbing water tank, with values of 274.3 kPa, 105.4 kPa, and 47.9 kPa, respectively.