Spectroscopic modeling and ultraviolet laser absorption spectroscopy measurements for the development of nonequilibrium thermometry and speciation diagnostics of for O2, NO and CN
Abstract/Contents
- Abstract
- Accurate spectroscopic modeling, when coupled with state-of-the-art laser diagnostics, enables quantitative measurements of the often poorly characterized nonequilibrium chemistry distinctive of hypersonic flows. The validation and improvement of existing chemical and fluid mechanical models that attempt to capture the complex molecular dynamics in such high-speed flows rely heavily on the temperature and concentration measurements delivered by laser-based sensors. The nonequilibrium thermochemistry that diatoms such as oxygen (O2), nitric oxide (NO), and the cyano-radical (CN) undergo requires high-fidelity experimental quantification, as these molecules and their internal energy distributions, rotational and vibrational, significantly impact the heat loads experienced by hypersonic vehicles. This dissertation will leverage the strong ultraviolet absorption spectra of the three aforementioned molecules, O2, NO, and CN, to develop a combination of laser diagnostics to probe the rotational and vibrational temperatures and species concentrations, both total and in specific vibrational quantum states. Low uncertainty, time-resolved measurements of such quantities provide invaluable data for the various modeling efforts to compare calculations against and improve model specific parameters. In this work, four sets of studies were undertaken to develop a spectroscopic model, use the model to inform temperature diagnostic wavelengths, perform an experimental spectroscopic validation, and finally demonstrate the accuracy of the diagnostic. Three major spectroscopic systems were modeled for the purposes of these works, the Schumann-Runge system, which give rise to the strong ultraviolet absorption spectrum of O2, the NO γ-bands, one of the strongest ultraviolet systems of NO, and the CN Violet system, one of the strongest molecular absorption systems in the ultraviolet. The developed models informed wavelengths that probed specific quantum states of the aforementioned diatoms and could be used in a two-color thermometry scheme to infer state-specific temperature and number density time histories in a shock tube environment. The experimental validation of the spectroscopic models at novel conditions and wavelengths improved the modeling capabilities and provides a framework for future spectroscopic studies that seek to further quantify the absorption spectra of air diatoms. Upon validating the spectroscopy, the laser diagnostics could be deployed to study the nonequilibrium chemistry of these diatoms behind strong shock waves and yielded quantitative temperature and concentration data critical to modeling heat loads experienced by hypersonic vehicles and the design of the thermal protection systems to withstand such loads.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2023; ©2023 |
| Publication date | 2023; 2023 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Krish, Ajay |
|---|---|
| Degree supervisor | Hanson, Ronald |
| Thesis advisor | Hanson, Ronald |
| Thesis advisor | Cappelli, Mark A. (Mark Antony) |
| Thesis advisor | Cruden, Brett, 1973- |
| Degree committee member | Cappelli, Mark A. (Mark Antony) |
| Degree committee member | Cruden, Brett, 1973- |
| Associated with | Stanford University, School of Engineering |
| Associated with | Stanford University, Department of Mechanical Engineering |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Ajay Krish. |
|---|---|
| Note | Submitted to the Department of Mechanical Engineering. |
| Thesis | Thesis Ph.D. Stanford University 2023. |
| Location | https://purl.stanford.edu/fp276qn0316 |
Access conditions
- Copyright
- © 2023 by Ajay Krish
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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