Date of Award

12-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Aeronautics and Astronautics

First Advisor

Robert Greendyke, PhD

Abstract

Thermal protection is required for vehicles entering planetary atmospheres to protect against the severe heating loads experienced. Characterization of candidate materials is often done utilizing plasma or arc-jet facilities, which provide steady-state testing of the thermal environments experienced during hypersonic flight, but do not correctly simulate hypersonic flowfields. Conversely, impulse facilities can reproduce flight velocities and enthalpies but have extremely short test times, prohibiting testing of thermal response. Modeling ablation and heating rates, particularly in the wake region, remains a significant challenge due to the complexity of the flowfield. To better understand this complex phenomenon and provide data to validate current computational models, experiments were conducted at the X2 expansion tunnel at the University of Queensland. Preheated strips of C-C and SiC-coated C-C were mounted in a two-dimensional compression wedge and tested in Earth entry ow. Calibrated spectral measurements were obtained in the near-stagnation and expansion regions targeting atomic Si, CN violet, C2 Swan, atomic N, atomic O, CO, and CO2 emissions for surface temperatures from approximately 1500 K to 2700 K. Emissions for C-C and SiC appeared similar in the near-stagnation region, increasing near the wall, while emissions for SiC-coated C-C displayed a distinct rise downstream of the shock, which suggests a higher concentration of ablative species. Comparisons were made to simulated results, which were conducted using the LAURA and HARA simulation codes following the process developed for this work. There was generally good agreement for CN emissions, which were most dominant, while the agreement was not as good for the other radiative phenomena investigated. It is believed that the underprediction of the ablation rate of the equilibrium-char model is a key factor.

AFIT Designator

AFIT-ENY-DS-18-D-035

DTIC Accession Number

AD1070521

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