The conditions governing the symptomatic behavior of a d.c. electric arc in a superimposed flow of gas are studied experimentally in an arc tunnel using a simplified electrode geometry. Special emphasis is placed on the parameter dependencies of the arc-flow-electrode interactions. The conditions leading to the transition from the steady mode to the restrike mode of arc operation are determined and found to be well correlated by a dimensionless grouping known as the Reynolds number. Arc visualization studies are reported. Variation of the anode arc terminus location is correlated with the independent arc parameters for the steady mode and leads to the development of a phenomenological model for the arc mode transition described. The model explains why an arc may suddenly jump from a smooth, quiescent operating condition to one where rapid, continuous fluctuations occur. The experiments demonstrate that the gasdynamic drag forces on an arc are significant. A magnetic body force is described which the authors contend is capable of counterbalancing the gasdynamic force and accounts for the heretofore unexplained stable location of the anode arc terminus observed experimentally with the steady mode. The experiments are conducted with argon, helium, nitrogen, and hydrogen for pressures between 50 and 760 mm Hg and entrance flow velocities from zero to over 100 m/sec. Anode to cathode spacings ranging from 2.5 to 7.5 mm are used, and the current is varied between 50 and 500 amp.Nomenclature C = arbitrary constant given by Eq. (3), kg-amp" 1 -^^" 1 -sec" 1 D = drag coefficient d = distance between double anodes, mm FD -gasdynamic drag force, N F m = magnetic body force, N I = arc current, amp P = pressure, torr T = radial distance from center of arc columns, mm R = radius of curvature, mm r c = radius of cathode column, mm r 0 -radius of anode column, mm Re = Reynolds number based on Se Res = Reynolds number based on S S = distance between cathode tip and anode, mm S e = effective anode column length, mm U = arc voltage, v V = velocity of superimposed flowfield, m-sec" 1 v = instantaneous velocity, m-sec" 1 x = distance from cathode tip, mm x s = distance from cathode tip to stable anode arc attachment location, mm y = distance from anode surface, mm p = gas density, kg-m~3 B = see Fig. 10 (f > = see Fig. 9 /z = dynamic viscosity, kg-m^-sec" 1 Ho = magnetic permeability of free space = 4?r X 10~7 Namp~2 5 = boundary-layer thickness, mm
