Experiments on heat transfer to HfB₂-SiC-based ceramics specimens in underexpanded supersonic flows of high-enthalpy nitrogen are performed on the VGU-4 induction high-frequency (HF) plasmatron of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The nitrogen plasma flows in the discharge channel of the plasmatron and the underexpanded dissociated-nitrogen flow past a cylindrical model with the ceramics specimen was simulated numerically within the framework of the Navier–Stokes and simplified Maxwell equations. Basing on the comparison of the experimental and calculated data the possible range of the effective coefficient of the heterogeneous nitrogen atom recombination on the ceramics surface is determined as a function of its total emissivity at a temperature of 2000°C. The microstructure and the element and phase compositions of the surfaces of the HfB₂-SiC-based ceramics specimens and the HfB₂-SiC-G-based ceramics specimen modified by two volume percents of graphene are studied after they have been subjected to the action of supersonic flow of partially dissociated nitrogen.

Experiments on heat transfer to a graphite specimen in supersonic underexpanded high-enthalpy nitrogen jets are conducted in the VGU-4 HF plasmatron of Institute for Problems in Mechanics of the Russian Academy of Sciences at the pressure in the low-pressure chamber of 8.5 hPa, the gas flow rate through the discharge channel of 3.6 g/s, and the HF generator power of 64 kW. Water-cooled conical nozzles with exit section diameters of 30, 40, and 50 mm were used. Numerical simulation of nitrogen plasma flow in the discharge channel of the plasmatron and flow of underexpanded dissociated nitrogen jet past a cylindrical sting with the graphite specimen is performed within the framework of Navier–Stokes equations and simplified Maxwell equations for the experimental conditions in supersonic regimes. From the comparison of the experimental and calculated data on the heat fluxes to the specimen surface the effective coefficient of heterogeneous nitrogen-atom recombination on the graphite surface is determined for the temperatures from 2273 to 2500 K.

The short-term (5 min) exposure to the supersonic flow of carbon dioxide plasma on ultrahigh-temperature ceramics of HfB₂-30vol.%SiC composition has been studied. It was shown that, when established on the surface at a temperature of 1615–1655 °C, the beginning of the formation of an oxidized layer takes place. Raman spectroscopy and scanning electron microscopy studies showed that the formation of a porous SiC-depleted region is not possible under the HfO₂-SiO₂ surface oxide layer. Numerical modeling based on the Navier–Stokes equations and experimental probe measurements of the test conditions were performed. The desirability of continuing systematic studies on the behavior of ultrahigh-temperature ZrB₂/HfB₂-SiC ceramics, including those doped with various components under the influence of high-enthalpy gas flows, was noted.

On the basis of the local modeling of heat transfer the parameters of supersonic flow past a cylindrical flat-nosed model in underexpanded dissociated carbon dioxide jets are recalculated to the case of spherical body entry into the Martian atmosphere on a wide range of the operating conditions of the VGU-4 plasmatron. The heat transfer parameters, similar in the experiment and hypersonic carbon dioxide flow past bodies are determined.

Numerical simulation of the flow of multicomponent nonequilibrium dissociated air past a water-cooled cylindrical model in underexpanded supersonic jets of high-enthalpy air is carried out within the framework of the Navier–Stokes equations using the stage-by-stage heterogeneous kinetics of interaction of dissociated air with the surfaces of β-cristobalite and copper and taking into account chemical reactions in flow for the conditions of experiments on heat transfer in the induction HF plasmatron VGU-4 (IPMech RAS). Numerical solutions for the chemical composition of the gas and for heat fluxes to the surface of the sensors are compared for various catalysis models. The contribution of diffusion and heat conduction processes to the heat flux to the surface is shown in various regimes of the interaction of gas with the surface material. The dependence of the flow characteristics (the chemical composition of the gas on the surface, the degree of filling of the surface, and the heat flux to the surface) on the density of adsorption sites has been determined. The modification of this dependence makes it possible to describe the entire range of the boundary conditions from non-catalytic to full catalytic ones.