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

The present 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, following cumulative shocks from multiple discharges, the flow deviates towards the plate electrode and transitions from a laminar to turbulent state, and negative corona discharge induces more intense deflection and disturbance compared to positive corona discharge.During a single discharge process, only a unidirectional EHD force towards the plate electrode is observed in positive corona discharge, while an additional scope of EHD force towards the pin electrode is found in negative corona discharge. Similarly, this phenomenon can be observed in a 2D fluid model simulation that disregards any disturbance to helium gas during transient discharging development. The simulation reveals that the evolution of EHD force follows a similar pattern as the discharge itself, which can be divided into three stages: development stage, stable stage and dissipation stage. The EHD force is scarcely observed during the dissipation stage. During the development stage, an EHD force towards the pin electrode is generated as the streamer approches the plate electrode. In the stable stage following a complete discharge, two EHD forces are observed towards both electrodes, with a spatial distribution structure of centrosymmetry presented in positive corona discharge. However, in negative cases, the EHD force towards the pin electrode is significantly smaller than that towards the other electrode. Through the analysis of spatial and temporal distribution of charged particles, it is determined that $\mathrm{O}_{2}{ }^{+}$ ions play a predominant role in generating the EHD force directed towards the pin electrodes in negative corona discharge. The reversal of local net charge polarity caused by Penning ionization and $\mathrm{O}_{2}{ }^{-}$ attachment further enhances this effect in negative corona discharge, highlighting the significance of polarity differences.