The electro-hydrodynamic force evolution in cross field pin to plate discharge with different voltage polarity

This paper presents experimental observations and simulation results on the interaction between plasma and gas flow in pin-to-plate corona discharge under different voltage polarities. Schlieren experiments reveal that during a single discharge process, only a unidirectional electro-hydrodynamic (EHD) force toward the plate electrode is observed in positive corona discharge, while an additional scope of EHD force toward the pin electrode is found in negative corona discharges. Similarly, this phenomenon can be observed in a 2D fluid model simulation that disregards any disturbance to helium gas during transient discharging development. The evolution of EHD force follows a similar pattern as the discharge itself, which can be divided into three stages. The EHD force is scarcely observed during the dissipation stage. During the development stage, an EHD force toward the pin electrode is generated as the streamer approaches the plate electrode. In the stable stage following a complete discharge, EHD forces toward both electrodes are observed, with a spatial distribution structure of centrosymmetry presented in positive corona discharges. However, in negative cases, the EHD force toward the pin electrode is significantly smaller than that toward the other electrode. Through the analysis of spatial and temporal distribution of charged particles, it is determined that O2+ ions play a predominant role in generating the EHD force directed toward the pin electrodes in negative corona discharges. The reversal of local net charge polarity caused by Penning ionization and attachment reactions producing negative ions further enhances this effect in negative corona discharges, thereby highlighting the polarity differences.