Simulation study of streamer propagation characteristics considering surface-attached and suspended bubbles under pulsed voltage

The thermal and cavitation effects of high-voltage pulsed discharge in water lead to the mixing of microbubbles into the background liquid, while the current theory of streamer discharge in the gas-liquid two-phase media remains to be improved. In this paper, a two-dimensional streamer discharge model with a surface-attached bubble and randomly distributed suspended bubbles was established by considering the field ionization and impact ionization dual-source terms, along with modified electron transport parameters, aiming to investigate the dynamic propagation characteristics of the streamer. The results indicate that the surface bubble contribute to the faster development of streamer with a wider channel radius. The gas composition and distribution of suspended bubbles significantly affects the velocity and morphology of the streamer. Depending on the variation in bubble size, the streamer shows three modes of development: nearly linear propagation, turning and branching. The propagation velocity of the streamer is affected by the weakening effect of charge accumulation and migration on the gas-liquid surface in conjunction with the enhancing effect of secondary electron avalanches inside the bubbles. Finally, taking the pre-breakdown time delay as an indicator, the favorable effect of microbubble environment on streamer development was verified by continuous discharge experiments at different frequencies. This work contributes to a better understanding of the nature of breakdown in gas-liquid two-phase media and provides theoretical guidance for bubble-assisted plasma discharge technologies.