Aero-Optical Effects in High-Enthalpy Flows

Abstract

Hypersonic flows present unique challenges to measurements made by sensors emittingelectromagnetic waves due to the complex interplay between fluid dynamics, thermodynamics, electrodynamics, atmospheric effects, and chemical reactions in the surrounding environment. In particular, the thermal nonequilibrium and turbulent nature of the flow field can cause both deflection and degradation of optical signals as they traverse the boundary layer, shock layer, and surrounding atmosphere. A comprehensive physical understanding of these phenomena is necessary to accurately assess and predict sensor performance in hypersonic environments. While prior research in Aero-Optical (AO) has predominantly focused on low-speed or low-enthalpy applications where perfect gas assumptions hold, this work investigates the influence of real gas effects and thermal nonequilibrium in high-enthalpy hypersonic flows. High-fidelity Computational Fluid Dynamics (CFD) simulations are employed to quantify the impact of these flow phenomena on optical signal propagation. Two representative cases are examined to explore different fidelity trade-offs: (i) a low-enthalpy, high-flow-resolution case, and (ii) a high-enthalpy, lower-flow-resolution case, where the modeling of chemical and thermal nonequilibrium is critical. To facilitate the analysis of AO distortions from CFD results, an open-source Python package, Hypersonics Aerodynamics Optics Tool (HAOT), was developed as part of this work. All results presented in this dissertation were obtained using HAOT version v1.1.3. This work advances the understanding of AO in high-enthalpy flows by investigating the behavior of AO properties in chemically and thermally nonequilibrium gases. It also examines the influence of internal energy level populations on AO using a State-to-State (StS) approach. In addition, this work includes the development of a computational package for analyzing AO in both high and low-enthalpy regimes under laminar and turbulent flow conditions. The dissertation can be found in https://github.com/mliza/dissertation, and the HAOT package can be found in https://haot.readthedocs.io/en/latest/.