Numerical Investigation of Humidity Effects on Positive Streamer Discharge at Sub-Atmospheric Pressure

In response to the increasing emphasis on green and low-carbon development, the rapid and in-depth progress of electrified transportation has made it a major focus in the construction of low-carbon transportation systems. To investigate the gas discharge mechanism of electrified transportation in complex environmental conditions, this research utilizes a two-dimensional axisymmetric fluid model to conduct a systematic analysis on the key features of positive streamer discharge under a sub-atmospheric pressure condition of 50 kPa, with relative humidity ranging from 0% to 90%. The results indicate that electron density exhibits an obvious nonlinear variation trend with increasing humidity: in the initial stage, water molecules enhance electron attachment, thereby reducing ionization efficiency; whereas under high humidity conditions, field-induced ionization dominated by space charge accumulation becomes predominant, further promoting the recovery of electron density. This study enriches the understanding of positive streamer discharge laws under sub atmospheric-pressure conditions, providing valuable theoretical references for research on gas discharge phenomena in special environment.