Effects of Ring Groove and Duty Cycle on Plasma Actuator Performance in High Speed Jets

Abstract

Localized arc filament plasma actuators (LAFPAs) have been used at The Gas Dynamics and Turbulence Laboratory (GDTL) for the purpose of controlling the downstream development of and noise radiation from a 1-inch (2.54-cm) nozzle exit diameter jet. The capability of LAFPAs for use in both subsonic and supersonic jets has been explored, and experiments to date have shown that these actuators have significant potential for mixing enhancement and noise control applications. While it has been established that the actuators manipulate instabilities of the jet, the mechanism by which the actuators interact with the instabilities is unclear. All of the results previously reported by GDTL have been based on a LAFPA housing (nozzle extension) which has an azimuthal groove of 1-mm width and 0.5mm depth along the inner surface. The ring groove was initially added to shield the plasma arcs from the high-speed jet flow. However, the effect of the ring groove on the actuation mechanism is not known. To explore this effect a new nozzle extension is designed, which relocates the electrodes to the nozzle extension face and eliminates the ring groove. Schlieren images, acoustic and particle image velocimetry (PIV) results of a Mach 0.9 jet of Reynolds number ~6.6×10 5 show that the same trends and magnitudes are achieved with and without a ring groove. Thus, it is concluded that the ring groove is not essential to the LAFPA control mechanism. Furthermore, the effect of the duty cycle of the actuator pulse on the LAFPA’s control is investigated. PIV results along with voltage and current traces of the plasma arcs show that the minimum duty cycle that provides complete plasma formation has the greatest control over the jet.