Impact of ablative materials on the plasma sheath structure and ionization behavior in hypersonic flows

Exploring the influence of material-coupled hypersonic plasma flow fields on radio-frequency (RF) communication environments holds significant engineering value. A three-dimensional hypersonic flow field is constructed based on the Navier-Stokes equations coupled with a 7-species, 18-reaction thermochemical model. The simulation considered multi-species transport, ionization reactions, and thermochemical nonequilibrium effects. The predicted axial distribution of peak electron density agrees well with NASA flight test data and previously published results, confirming the accuracy and applicability of the proposed model. The spatiotemporal evolution of the plasma sheath is systematically investigated, with a focus on three representative ablative materials: carbon-carbon composites (C-C), silicon-based thermal protection materials (Si-Phenolic Resin, Si-PR), and aluminum matrix composites (AMCs). Based on this, distributions of electron number density, collision frequency, and flow field temperature are obtained at two representative reentry altitudes, revealing the coupled effects of ablation composition, thermal radiation, and product transport on sheath structure. The results indicate that along the axial direction of the vehicle, the C-C material exhibits the highest ionization near the stagnation point, Si-PR maintains strong ionization activity in the midsection, and AMCs show favorable thermal diffusion capability in the rear region. Based on the quantitative distribution characteristics of electron density and collision frequency, a region-specific material adaptation strategy is proposed. This strategy provides theoretical guidance for thermal protection material design and enhances the understanding of material selection and layout optimization in the electromagnetic environment design of reentry vehicles.