Study of the physical pattern of the discharge between cold electrodes in a supersonic seeded plasma jet

Abstract

structural elements, especially the electrodes. Cooling of the electrodes leads to the seeded-gas temperature near the electrodes being considerably lower than that in the core flow. The conductivity of a seeded gas decreases markedly with temperature decrease, and the boundary layer regions immediately adjacent to the electrodes becomes practically electrically nonconductive. The mechanism of current penetration through the boundary layes on electrodes in a supersonic seeded plasma flow was studied experimentally. 1. Boundary layer stmetttre at the eleel~odes. During supersonic flow past a cold electrode, a boundary layer develops on the electrode and the gas temperature in the boundary layer changes rapidly from the core flow temperature T.o to the electrode temperature T w. As a typical example we consider the flow of air with an ionized seed-potass ium-having the following parameters: stagnation temperature T O = 5000"K; stagnation pressure Po = 10 aim abs; static pressure p,~ = 0.2 aim abs; M = 8; static temperature T,o = 3000~ seed concentration K ~ 1-2%. In the absence of electric and magnetic fields, assuming the boundary layer on the electrodes to be laminar, we can use the known theoretical solution for the boundary layer on a flat wall from [1] for estimates. We call the sublayer of thickness 6, where T -< T,o, the "cold" boundary 1ayes sublayer. Calculations of the physical thickness of this sublayer at a distance of about 100 mm from the leading edge for a wall temperature T w = T.o/4 yields the value 6 ~ 0.6 ram.