Characterization of Plasma Formation and Induced Flows of Nanosecond-Pulsed Dielectric Barrier Discharges for Use in Supersonic Flow Control
Over the past few decades, the use of plasma actuators as flow control devices has been a growing field in aerodynamics. Dielectric barrier discharges (DBDs) are a subset of these actuators, and have been shown to have the ability to reattach separated flow. These DBDs are typically driven by one of two waveforms: an AC waveform or a series of high voltage nanosecond pulses. Ac driven DBDs have proven to be effective in low speed flows, while nanosecond pulsed DBDs are believed to offer more potential for applications in high-speed flow as they utilize a different flow control mechanism. This thesis will focus on nanosecond pulsed DBDs. One of the main goals of current work with nanosecond pulsed DBDs is achieving supersonic flow control. A number of groups are attempting to achieve this goal, specifically the control of oblique shock waves. In order to accomplish the goal of supersonic flow control, it is crucial that the dynamics of the plasma and the flow it produced be well understood. There have been previous studies into these features, but there remain some areas that need to be investigated. Initial experiments in this work investigate the effect of pulse duration on the discharge mode for a nanosecond-pulsed dielectric barrier discharge plasma actuator. It has been shown that pulse repetition frequency and applied voltage contribute to transition from uniform to filamentary discharge. However, little primary investigation has been conducted to study the effect of pulse duration. Results indicate that increasing pulse duration while maintaining constant applied voltage and repetition frequency can still assist in transition of discharge mode. Temporal resolution is achieved by monitoring the camera gate along with the rise of the voltage. Following the investigation of the plasma formation, induced flows of numerous waveforms were recorded using high-speed schlieren imaging. These videos offer new insight into the development of the induced flow produced by nanosecond pulsed DBDs and what effects various waveforms have on the flow. In particular, changing pulse repetition frequency shows a dramatic change in the induced flow. The end goal of characterization of plasma formation and induced flow is the application to supersonic flow control. High pulse duration and high repetition frequency pulses were used in an attempt to alter an oblique shock wave generated by a 25° compression ramp in a Mach 2 flow. Change in the oblique shock was not observed for any test case, likely due to the fact that filamentary breakdown, which is believed to be crucial for high-speed flow control, was not maintained once the tunnel was in use.
Bane, Purdue University.
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