Numerical Investigation of High-Enthalpy Effects on Aero-Optics in Hypersonic Flows

Hypersonic flows exhibit high complexity, encompassing high-enthalpy, reactive flows (involving chemistry), energy transfer between molecular energy modes, turbulence, boundary layers, unsteadiness, and shocks. These factors can directly or indirectly affect and degrade optical signals as they propagate through the medium. While previous aero-optics research has typically relied on perfect gas assumptions suitable for low-speed, low-enthalpy flows, this study explores real-gas behavior in hypersonic regimes. It addresses three primary objectives: the effect of chemical reactions on polarizability, the behavior of optical properties such as the index of refraction and dielectric constant, and the influence of Reynolds-averaged Navier–Stokes-fidelity turbulence on the flowfield. The results show that polarizability is not solely a function of signal frequency but is also influenced by a molecule’s internal energy state, particularly vibrational modes. Although high-energy vibrational states are affected by non-Boltzmann distributions, their influence on overall polarizability is minimal. Additionally, the Gladstone–Dale constant is tied to species distributions, which may require a two-temperature model for accurate characterization. The index of refraction and dielectric constant are strongly correlated with flow density. These findings advance aero-optical modeling for hypersonic applications and emphasize the need to incorporate nonequilibrium effects for accurate prediction and system design.