The RailPAc arc

Gray, Miles Dalbom
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This dissertation will detail work examining the plasma arc of the RailPAc magnetohydrodynamic flow actuator. Initial studies of the RailPAc arc have shown that the arc formation and propagation processes are highly stochastic and in many cases unpredictable. This insight motivated most of the work in this dissertation to better understand the nature of arc propagation, towards the design of a predictable and well behaved high intensity gliding arc. The work consists of several experiment based studies examining the RailPAc plasma arc, focusing on electrical characterization, spectroscopic temperature analysis, narrow-band-imaging species evolution within the arc, and the effects of electrode surface oxidation states on the propagation of the arc. Additional experimental studies examined the effects of external magnetic fields and rod configurations, the effect of the wall near the electrodes, as well as long term damage on copper and elkonite electrodes. Computational studies examined phenomena which were difficult or not possible to characterize experimentally. This includes mechanisms of wall stabilization, root mobility over oxidized surfaces, and simulations of the arc column in two and three dimensions to examine coupling of the arc to surrounding gas. The key contributions of this work can be split into two parts, both of which have experimental and computational components. The first is the characterization of the RailPAc arc dynamics (electrically, chemically, and physically) and its coupling to the surrounding flow. This is examined experimentally with spectroscopy, high-speed narrow-band imaging, and electrical measurements, as well as computationally with commercial arc modeling software solving fluid flow coupled to Maxwell’s equations in potential form. The second is the examination of the RailPAc arc root interaction with the electrode surface, particularly the anode root which has seen very little examination compared to the cathode in previous research efforts directed at high intensity gliding arcs. Both of these are combined in a computational effort to model the RailPAc arc column in two and three dimensions.