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Title:Active control of supersonic boundary layers using electric arc plasma actuators
Author(s):Ostman, Rebecca
Advisor(s):Dutton, J. Craig; Elliott, Gregory S.
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Plasma actuators
Flow control
Abstract: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 Arc Filament 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, trigger circuit, which creates an arc discharge between the trigger electrode and anode, pre-ionizing the gas between the electrodes to facilitate the second arc discharge. The second circuit is a high-current, arcsustaining circuit, which creates an arc between the cathode and the anode. The electrodes are all contained within a cavity that has a small orifice leading into the flow. When the arc discharges into the cavity, 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, making this 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 single pulse on the boundary layer was studied. Voltage measurements were obtained, which showed that the voltage required for the trigger breakdown was about 3.4 kV, and the arc-sustaining circuit was charged to a potential of 565 V. These measurements also showed that the timing and consistency of the discharges were much improved in the low pressure environment of the Mach 3 crossflow as compared to when the actuator was operated in quiescent, atmospheric conditions. PIV measurements were also obtained and these showed that the PPJ has a very modest effect on the boundary layer. These measurements 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 the maximum penetration of the jet into the crossflow was about 1.33δ. There was also some evidence in the Reynolds shear stress measurements that some backflow occurred just behind the jet orifice, especially at the 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 the span of the wind tunnel, and each actuator consisted of two electrodes set in small cavities recessed from the surface, but open to it. For most of the experiments, the current through the actuators was 1 A, and voltage measurements revealed that approximately 4.5 kV were required to initiate the breakdown between the electrodes. The LAFPAs were studied in two different flow situations: a boundary layer over a flat surface and a boundary layer over a 5º diverging ramp. iii Schlieren 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 the position 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 had very minimal effects on the boundary layer over both the flat wall and the diverging ramp. Practically no difference in the streamwise velocity was visible between the control and no control cases, regardless of frequency of operation and delay time after the initiation of arc breakdown. The blast wave created by the LAFPAs is visible in the transverse velocity measurements, and it grows in time and is pushed downstream by the crossflow. This blast wave becomes weaker with increasing frequency. A plume of hot gas is also visible, emanating from the actuator cavities, at early delay times. This plume dissipates very 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 the strength of the blast wave and hot gas plume, but again they followed the trend of decreasing strength with increasing frequency. Overall, the effects of the LAFPAs on the supersonic flows studied here were minimal.
Issue Date:2014-01-16
Rights Information:Copyright 2013 Rebecca Jeane Ostman
Date Available in IDEALS:2014-01-16
Date Deposited:2013-12

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