Simulation and experimental study on the synergistic effect of humidity and applied voltage on negative DC streamer discharge in short air gaps

Abstract The influence of humidity and applied voltage on negative streamer discharge in air gaps exhibits a nonlinear synergistic effect. Numerical simulation and experimental investigation were conducted on negative streamer discharges in a 3 mm needle–plane air gap. A fluid model was established that simultaneously accounts for both humidity and the applied voltage. The validity of the model was confirmed by comparison with experimental data. The electron density and electric field at the streamer head increase with increasing humidity, and both quantities continue to intensify as the streamer propagates toward the plane electrode. The magnitude of the applied negative DC voltage and its influence become more pronounced in the vicinity of the plane electrode. The applied voltage has almost no effect on the streamer channel radius, whereas the channel radius increases with increasing humidity. When the applied voltage amplitude is below 10 kV, an increase of 30% in relative humidity leads to approximately a 10% reduction in streamer propagation velocity, while the discharge current exhibits only minor variation. In contrast, when the applied voltage amplitude exceeds 10 kV, every 30% increase in relative humidity causes the electric field at the streamer head, the streamer channel radius, and the streamer propagation velocity to increase by 7.8%, 10%, and 50%, respectively, and the discharge current nearly doubles. At constant relative humidity, every additional 1 kV in applied voltage increases the electric field at the streamer head, the streamer propagation velocity, and the discharge current by approximately 5%, 25%, and 30%, respectively. Moreover, these increasing trends become more pronounced at higher relative humidity. However, the increase in applied voltage has no significant effect on the streamer channel radius.