Investigation of freestream plasma flow produced by inductively coupled plasma wind tunnel

The freestream air plasma jet produced by the Plasmatron facility at the von Kármán Institute for Fluid Dynamics is investigated. Intrusive and nonintrusive measurement techniques are combined to characterize the plasma flow at pressures between 1500 and 20,000 Pa and electrical power between 120 and 300 KW, covering a broad range of atmospheric entry conditions relevant for thermal protection systems testing. The high-speed camera imaging technique is applied to investigate the unsteadiness features of the plasma jet, and a novel frequency-spatial-domain elaboration procedure is proposed. The results show that the power supply ripple and the test chamber static pressure are the main driving parameters of the plasma jet unsteadiness. The optical emission spectroscopy measurement allow the conclusion that the freestream flow is in local thermochemical equilibrium in nearly the whole operating envelope investigated. Comparison between spectroscopy measurement and freestream temperature calculations based on intrusive techniques show that the surface catalytic efficiency of the cold-wall copper sensors used to measure heat flux is close to 10-2. This catalytic property is found to increase with the freestream temperature for the lowest pressure condition investigated.