Characterization of the VKI Plasmatron subsonic ICP jet combining optical emission spectroscopy, intrusive measurements, and CFD simulations

This paper addresses the characterization of the subsonic flow in the 1.2~MW Inductively Coupled Plasma (ICP) wind tunnel at the von Karman Institute for Fluid Dynamics (VKI), targeting chamber pressures of 50 and 100~mbar, and input electric powers between 150 and 300~kW. Ultraviolet to near-infrared optical emission spectroscopy measurements of the free-jet flow are carried out with an updated experimental set-up, calibration procedure, and data processing, providing high-quality absolute spatially-resolved emission spectra. Emission measurements agree with thermochemical equilibrium predictions within a range of conditions, allowing to extract experimental maps of cold-wall heat flux and dynamic pressure against the inferred free-jet enthalpy. A detailed comparison with the characterization methodology traditionally employed is presented, highlighting the need for an improved modeling strategy. Using the measured free-jet temperature and dynamic pressure only, a forward procedure for the computation of the stagnation line flow is proposed. The latter agrees with intrusive heat flux measurements through a range of test conditions, and for values of the recombination coefficient of the reference copper probe commonly found in the literature. Results demonstrate that a consistent framework between numerical simulations and experimental data can be achieved, defining an improved framework for the characterization of the subsonic ICP jet.