Characterization of Localized Arc Filament Plasma Actuators Used for High-speed Flow Control

Abstract

The paper discusses development and characterization of localized arc filament plasma actuators and their use to control high-speed and high Reynolds number jet flows. Multiple plasma actuators (up to 8) are controlled using a custom-built 8-channel high-voltage pulsed plasma generator. The plasma generator independently controls pulse repetition rate (0 to 200 kHz), duty cycle, and phase for each individual actuator. Current and voltage measurements demonstrated the power consumption of each actuator to be quite low (20 W at 20% duty cycle). Plasma power budget for 8 actuators is approximately 0.6% of the flow power. Emission spectroscopy temperature measurements in the pulsed arc filament showed rapid temperature increase over the first 10-20 µsec of arc operation, from below 1000 0 C to up to about 2000 0 C. At longer discharge pulse durations, 20-100 µsec, the plasma temperature levels off at approximately 2000 0 C. The pulsed plasma temperature measurements provide key input data for ongoing and future CFD modeling of a high-speed flow forcing by the actuators. Preliminary modeling calculations using an unsteady, quasi-one-dimensional arc filament model showed that rapid localized heating in the arc filament on a microsecond time scale generates strong compression waves. The results of calculations also suggest that flow forcing is most efficient at low actuator duty cycles, with short heating periods and sufficiently long delays between the pulses to allow for convective cooling of high-temperature filaments. The model predictions are consistent with laser sheet scattering flow visualization results and particle imaging velocimetry measurements. These measurements show large-scale coherent structure formation and considerable mixing enhancement in an ideally expanded Mach 1.3 jet forced by eight repetitively pulsed plasma actuators. The effects of forcing are most significant near the jet preferred mode frequency (ν=5 kHz). The results also show a substantial reduction in the jet potential core length and a significant increase in the jet Mach number decay rate beyond the end of potential core, especially at low actuator duty cycles.