Considerations on a free-streamcharacterization procedure for plasma jet ofthe VKI Plasmatron facility

A procedure combining Optical Emission Spectroscopy measurements (OESm) and one-dimensional stagnation line computations has been recently presented, demonstrating the reconciliation of experiments and boundary layer simulations within a range of Plasmatron operating conditions. This work discusses one aspect of the procedure, namely the selection of the inlet point of numerical simulations, by incorporating additional measurements and a sensitivity study. Experiments are carried out at a single static pressure in the chamber and three different electrical powers. Temperature profiles are extracted from OESm at three locations along the jet centerline: 335, 375, and 385 mm from the torch exit in free stream conditions, and at 335, 375 mm with the heat flux probe injected at 385 mm. Pitot and temperature measurements at 335 and 385 mm estimate the velocity. The article analyzes how to combine these measurements to define the inlet condition for the quasi-one-dimensional simulations that numerically replicate the experimental heat flux at a user-selected catalytic coefficient $. Results indicate that selecting the inlet at two times the probe radius and imposing the measured temperature at 375 mm and the velocity at 385 mm provides a good compromise. This configuration yields numerical estimations that are consistent with the experimental heat flux for $ ≈ 0.01, consistent with the original formulation of the procedure.