Radio frequency (RF) blackout during atmospheric reentry leads to the cutoff of communication with ground stations and/or data-relay satellites. This causes significant problems during reentry, and thus, mitigation methods have been in high demand. In this study, we numerically demonstrate a novel method for mitigating the RF blackout using surface catalysis effects. Plasma flow behavior and electromagnetic wave propagation around a reentry vehicle were investigated in detail. The approach couples computational fluid dynamics and a frequency-dependent finite-difference time-domain method. The computations were performed with a massive parallelization technique using a large computer. The computed results were compared for cases imposing low and full catalysis conditions on a surface boundary. The investigation revealed that the surface catalysis effects reduce the RF blackout. Atomic species, dissociated across a shock wave formed in front of the vehicle, were recombined on the vehicle surface through surface catalysis. These molecules, flowing into a wake region at the vehicle's rear, caused recombinations of electrons, originally generated in the shock layer. Therefore, a decrease in electrons was observed in the wake region and a wake path, which allows the propagation of electromagnetic waves, was formed. This complicated behavior of the molecules and electrons, induced by the surface catalysis, resulted in mitigation of the RF blackout.
The flow enthalpy of an arc-heated wind tunnel is an important parameter for reproducing planetary entry and performing heating tests. However, its distribution is insufficiently clarified owing to complicated phenomena, such as arc discharge and supersonic expansion. In this study, we assess the enthalpy of an arc-heated flow in a large-scale facility based on measurements and computational results. The flow enthalpy of high-temperature gases, which comprised thermal, chemical, kinetic, and pressure components, was reconstructed based on the measured rotational temperature, heat flux, and impact pressure, in addition to the computational science approach. The rotational temperature of nitric oxide molecules was obtained using emission spectroscopic measurements of band spectra in the near-ultraviolet range. A numerical model was developed and validated based on measured data. The results indicated that the model efficiently reproduced the arc discharge behavior in the heating section and the thermochemical non-equilibrium in the expansion section. It was discovered that the dominant components of the arc-heated flow in the test section were the chemical and kinetic components. The flow enthalpy exhibited a non-uniform distribution in the radial direction. We conclude that the flow enthalpy of the core is approximately 28 MJ/kg at the nozzle exit.
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