Experimental and Numerical Simulation of the Heat Transfer of the UHTC Surface in Underexpanded Dissociated Nitrogen Jets

Experiments on heat transfer in supersonic underexpanded jets of high-enthalpy nitrogen with ceramic samples based on HfB2–SiC are carried out at the induction RF plasmatron VGU-4 (Ishlinsky Institute for Problems in Mechanics of the Russian Academy of Sciences) at a pressure in the pressure chamber of 8.5 hPa, a gas flow rate through the discharge channel of 3.6 g/s, and an RF power of the plasma torch generator for anode supply of 64 kW. Three heat transfer modes are implemented using water-cooled conical nozzles with outlet diameters of 30, 40, and 50 mm. For the experimental conditions in supersonic modes, using a numerical method within the framework of the Navier–Stokes equations and simplified Maxwell equations, we simulate nitrogen plasma flows in a plasmatron discharge channel and the flow of dissociated nitrogen underexpanded jets around a cylindrical holder with a ceramic sample. From a comparison of the experimental and calculated data on heat fluxes to the surface of three samples, the effective coefficient of heterogeneous recombination of nitrogen atoms on the surface of ultra-high-temperature ceramics (UHTCs) at temperatures of 2273–2843 K is determined.