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Title:Using Ultraviolet Laser Absorption Spectroscopy To Measure Vibrational Temperature Time Histories Of Shock-heated Oxygen
Author(s):Krish, Ajay
Contributor(s):Hanson, Ron K; Streicher, Jesse William
Subject(s):Spectroscopy as an analytical tool
Abstract:Here, a two-color O$_{2}$ vibrational temperature diagnostic was developed by utilizing spectroscopic models to inform optimal wavelength candidates for both a continuous-wave (CW), ultraviolet (UV) laser and a picosecond pulsed, UV laser. Cross-sections of shock-heated O$_{2}$ were measured using a CW UV laser, and results over a range of wavelengths and temperatures are compared against a Stanford model, developed to simulate oxygen absorption cross-sections in the Schumann-Runge system under vibrational non-equilibrium conditions, and Specair, a spectroscopic model for high-temperature air species developed by Laux et al. All measurements were completed behind reflected shocks in 2\% and 5\% O$_{2}$ in argon (Ar) mixtures. Vibrational temperatures for cross-section measurements were calculated for plateaus and peaks in experimental absorbances using a Bethe-Teller relaxation model up to 6,000 K and a steady-state approach above 6,000 K. Temperature sweep measurements were fixed around 223.237 nm, while wavelength sweep measurements were taken around 4550 K and ranged between 223.23 nm to 223.27 nm. Temperature sweep cross-sections agree to within 15\% of Specair modeled cross-sections, with most measurements falling within 10\% of Specair predictions. Wavelength sweep cross-sections agree at shorter wavelengths with Specair cross-sections, but longer wavelength features are offset from both the Stanford model and Specair predictions. Using the spectroscopic model developed here to inform appropriate wavelength selection, the UV laser systems in this work become tools for directly tracking both vibrational temperature and populations in specific vibrational states of O$_{2}$ as it undergoes vibrational relaxation and dissociation behind strong shock waves. These temperature and population time histories provide important experimental data needed to evaluate current computational models that seek to capture the molecular energy transfer present in high-enthalpy airflows.
Issue Date:2021-06-25
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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