The instability of electric arcs burning axially in accelerated flow

Abstract

Experiments with electric arcs in an expansion tube fitted with a plane-symmetric converging nozzle section have demonstrated that the arc in accelerating flow is inherently unstable. An axisymmetric disturbance is generated which tends to develop into a helical mode in downstream regions. The evidence suggests that the source of instability is the shear layer between the cold flow and the hot, more highly accelerated arc column. For flows at low Reynolds number (<100) the arc column may be regarded as stable and its measured properties then lie close to the theoretical steady-state characteristic.

Experiments and modeling of an instability of an atmospheric pressure arc

“…In Ref. 13, an experimental investigation of a 20-500 A ac arc in accelerating flow revealed similarities with the instabilities seen in fluid jets. The work concludes that the instabilities arose from the shear layers between the cold gas flow and the more accelerated plasma of the arc column.…”

Electron Density Measurements in UV-Preionized XeCl and CO2 Laser Gas Mixtures

“…the source of excitation is identified with the evaporation of electrode material. In the case of the low-current arcs of Howatson and Topham (1976), the source of the excitation is not clear, but small pressure reflections within the nozzle are a possibility, as are disturbances shed from the upstream electrode. In the accelerating flows the clearly defined axisymmetric deformations observed were sustained for about one wavelength before breaking down into a random structure.…”

“…These symmetric disturbances are found to occur when the heated gas has been subjected to an axial acceleration such as is produced by a convergent nozzle. Howatson and Topham (1976) compared the stability of low current arcs in a series of accelerated flows with constant pressure flows of comparable speed, and found that flow acceleration was a necessary condition for instability. The frequency of the varicose oscillations was found to be close to the mean velocity gradient of the accelerating flow.…”

Acetylacetonebis(acetylacetonato)dioxouranium(VI)

“…Earlier studies of uranyl complexes with chelating agents like HCOO-, acac-, ac-and C2 O2-have shown the coordination of U to be bipyramidal with a linear UO 2 group and five (Frasson, Bombieri & Panattoni, 1966;Howatson &Grev, 1975;Mentzen, Puaux & Sautereau, 1978) or occasionally six (Alcock, 1973;Jayadevan, Singh Mudher & Chackraburtty, 1975) O atoms arranged equatorially. The present investigation was undertaken to find out how the title complex conforms to this pattern.…”