针–板电极下水中亚音速流注形态与发展过程

Morphology and Development of Underwater Subsonic Streamer Under Needle to Plane Electrodes

为了研究针–板电极形式下的水中亚音速流注形态及发展过程的机理,该文建立了水中流注放电综合观测平台,并从微观物理的角度,探讨了电压极性对流注形态的影响。流注的起始阶段可分为：电极尖端液体介质的密度扰动、微气泡的形成和以微气泡为基础的流注形成。阴、阳极流注的差异在于流注形态和传播方式的不同。对于阳极流注,其形态在传播过程中会发生变化：在大部分时间内以气泡簇的形式缓慢的生长（20~80m/s）;在发展最后阶段,气泡簇顶端生长出树状亮流注（第二类流注）,以极高的速度传播（（29）30km/s）。对于阴极流注,其形态为多分叉的树枝状亮流注,发展方式为周期性的分叉生长,平均流注发展速度约100~350m/s,并在最后阶段有明显的速度抬升。电子和离子迁移率巨大的差距,以及沉积电荷引起的界面不稳定性,造成了显著的极性效应,使得阴极流注的起始电压更高,传播速度更快,形态更加发散。

An integrated observation platform for underwater streamer discharge were established in order to study the mechanism of underwater subsonic streamer morphology and development. The polarity effect on the streamer morphology and development was analyzed from the perspective of microphysics. The initial stage of streamer development can be divided into： density fluctuation of liquid around electrode tip, micro-bubble initiation and streamer initiation from the micro-bubble. The difference between the positive and negative streamers lies in the streamer morphology and development process. The morphology of positive streamer goes a transition process. The positive streamer propagates in the shape of bubble cluster with a low speed（20~80 m/s） at the most time. However, at the final stage, a tree-like luminous streamer（secondary streamer） is formed on the bubble cluster tip propagating in a very fast speed（（29） 30 km/s）. The negative streamer has a tree-like structure with numerous filaments. The negative streamer develops in a period branching mode with a speed of 100~350 m/s. At the final stage of the negative streamer development, there is a remarkable increase of the streamer velocity. The distinct difference between the mobility of electron and ion, and the interface instability caused by deposited charges results in the polarity effect which leads to higher initiation voltage, propagation speed and divergent shape of the negative streamer.