Performance recovery of plasma actuators in wet conditions

Plasma actuators have been extensively studied for flow control applications over the past two and a half decades. While these studies have been traditionally focused on characterizing their performances as flow control devices, the performance of plasma actuators under adverse conditions such as dew or light rain remains to be less explored. This paper seeks to study the effects of water adhesion from droplets directly sprayed on to a plasma actuator using thrust recovery as the performance metric. It was found in all tests that wet actuators quickly recover plasma glow, before gradually regaining performance comparable to the dry actuator. The measured thrust for the wet actuator after 5 s of operation recovered by 46% and 42% of the thrust of the dry actuator for 50.0-62.5 g m^-2 and 125-150 g m^-2 of sprayed water droplets, respectively. At 22.5 kV_pp and 14 kHz, the highest thrust recovery was recorded at 84% of that of the dry actuator after 80 s of operation. For 17.5 kV_pp and 14 kHz the wet thrust recovered by 79%, while for 22.5 kV_pp and 10 kHz the wet thrust recovered by 68% of their dry counterpart in 80 s. For 17.5 kV_pp and 14 kHz, the thrust almost fully recovered in comparison to the dry actuator after about 290 s of operation. These results indicate that both applied voltage and operating frequency plays a critical role in the performance recovery while the latter may have a stronger influence. Performance recovery for a wet serpentine shaped plasma actuator is also included for general applicability. The power data in all cases show that wet actuators consume more power which with time gradually approach the dry actuator power data. This is because during the initial stages of operation, the rolling mean current of the wet actuator is higher than the dry actuator even though the ionization spikes of dry actuator is stronger.