Active control of supersonic boundary layers using electric arc plasma actuators

Plasma actuators;Flow control

Ostman, Rebecca ; Dutton ; J. Craig ; Elliott ; Gregory S.

关键词: Plasma actuators;    Flow control;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/46623/Rebecca_Ostman.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Flow control, especially active control, has potential to vastly improve aerospace vehicles in terms of both efficiency and performance. Plasma actuators are a promising technology because they have no moving parts, fast response rates, and they can be forced at a wide range of frequencies. The two plasma actuators studied in this work are a Pulsed Plasma Jet (PPJ) and an array of Localized ArcFilament Plasma Actuators (LAFPAs), which both have shown promise for supersonic applications.The PPJ design consists of three electrodes and two circuits. One circuit is a high-voltage, triggercircuit, which creates an arc discharge between the trigger electrode and anode, pre-ionizing the gasbetween the electrodes to facilitate the second arc discharge. The second circuit is a high-current, arcsustainingcircuit, which creates an arc between the cathode and the anode. The electrodes are allcontained within a cavity that has a small orifice leading into the flow. When the arc discharges into thecavity, it heats and pressurizes the air within the cavity, which is then exhausted through the orifice.When the discharge ends, the cavity cools and draws air back into it, to reset it for the next cycle, makingthis a zero-net-mass-flux device, or a synthetic jet.For this investigation, a single PPJ was placed in a Mach 3 crossflow, and the effect of a singlepulse on the boundary layer was studied. Voltage measurements were obtained, which showed that thevoltage required for the trigger breakdown was about 3.4 kV, and the arc-sustaining circuit was chargedto a potential of 565 V. These measurements also showed that the timing and consistency of thedischarges were much improved in the low pressure environment of the Mach 3 crossflow as compared towhen the actuator was operated in quiescent, atmospheric conditions. PIV measurements were alsoobtained and these showed that the PPJ has a very modest effect on the boundary layer. Thesemeasurements showed that the PPJ fluctuates in strength over the course of a single pulse. This‘chugging’ behavior is believed to be due to complex wave dynamics and reflections within the cavity.The maximum transverse velocity achieved by the jet was about 9.8% of the freestream velocity, and themaximum penetration of the jet into the crossflow was about 1.33δ. There was also some evidence in theReynolds shear stress measurements that some backflow occurred just behind the jet orifice, especially atthe times when the outward velocity was lowest, indicating that the cavity refilled at those times.The LAFPA array used in this investigation consisted of four actuators evenly spaced along thespan of the wind tunnel, and each actuator consisted of two electrodes set in small cavities recessed fromthe surface, but open to it. For most of the experiments, the current through the actuators was 1 A, andvoltage measurements revealed that approximately 4.5 kV were required to initiate the breakdownbetween the electrodes. The LAFPAs were studied in two different flow situations: a boundary layer overa flat surface and a boundary layer over a 5º diverging ramp.iiiSchlieren imaging was used to investigate the LAFPA’s effects on the stability of a normal shock.It was determined that actuation had virtually no effect on either the mean or standard deviation of theposition of the normal shock, for either of the boundary layer configurations and regardless of stagnationto-exit pressure ratio.PIV was used to study the LAFPA’s effects on the boundary layer. The LAFPAs once again hadvery minimal effects on the boundary layer over both the flat wall and the diverging ramp. Practically nodifference in the streamwise velocity was visible between the control and no control cases, regardless offrequency of operation and delay time after the initiation of arc breakdown. The blast wave created by theLAFPAs is visible in the transverse velocity measurements, and it grows in time and is pusheddownstream by the crossflow. This blast wave becomes weaker with increasing frequency. A plume ofhot gas is also visible, emanating from the actuator cavities, at early delay times. This plume dissipatesvery quickly, is not observed to move downstream, and follows the same trend as the blast wave,becoming weaker with increasing frequency. Increasing the current from 1 A to 4 A increased thestrength of the blast wave and hot gas plume, but again they followed the trend of decreasing strengthwith increasing frequency. Overall, the effects of the LAFPAs on the supersonic flows studied here wereminimal.