Arc-Generated Flow Phenomena in Repetitively Pulsed Gas-Flow Spark Gaps

Flow phenomena occurring in repetitively pulsed gas-flow spark gaps have been investigated experimentally and compared with theory. Optical flow diagnostics were obtained after the current pulse using schlieren photography, a flashlamp, and a framing image converter camera (ICC). Experimental results reveal nearly spherical arc-generated shocks propagating symmetrically with respect to the arc debris center. Supersonic shocks rapidly weaken into acoustic disturbances. Heated arc debris convects at the undisturbed gas velocity, while turbulent debris spreading causes a linear growth of the heated gas region radius at a velocity of 10-40 m/s. At low flow velocity (15 m/s), the upstream edge of the heated arc debris remains at a constant streamwise position until 700 μs after the arc, and then moves downstream at constant velocity. This delay time before downstream motion begins is reduced to 38 μs for gas velocities of 35 m/s. Numerical results qualitatively agree with experiments, where heated gas is predicted to convect at the undisturbed gas velocity. The shocks, which initially propagate at high Mach number, rapidly slow to acoustic speed.