Velocity and temperature of plasma jets and their change due to artificial optical inhomogeneities introduced into plasma

A method to measure the velocity of subsonic submerged plasma jets with unstable flows based on an analysis of the motion of optical inhomogeneities introduced into the jet is considered. A source of these inhomogeneities in the form of a heat-resistant thin rod is placed in a diametrical direction of a chosen cross section of the jet flowing from the output channel of a high-current DC plasmatron into ambient air under atmospheric pressure. The plasma-forming gas is a mixture of argon and nitrogen, and the characteristic Reynolds numbers of the studied flows are $\mathrm{Re}_D = 50$–$300$. The perturbation effect of the body introduced into the plasma jet on the two most important characteristics (plasma temperature and velocity) was studied. Specific features of laminar and pulsating flows of submerged plasma jets were studied via two-site, highspeed, synchronous visualization. It is shown that the length of the continuity restoration part of the jet flowing around the rod at a temperature of $10$–$12$ kK and a velocity of $100$–$500$ m/s is very small (several millimeters) under these conditions. The plasma temperature in the region of the strongest thermal perturbation caused by the introduction of the rod was measured with spectral methods. The observed plasma cooling is compared with the calculated decrease in the enthalpy due to expenditures for the heating and ablation of the rod material.