Unbiased Filtered Rayleigh Scattering Measurement Model for Aerodynamic Flows
| dc.contributor.author | Warner, Evan Patrick | en |
| dc.contributor.committeechair | Lowe, Kevin T. | en |
| dc.contributor.committeemember | Paterson, Eric G. | en |
| dc.contributor.committeemember | Nguyen, Vinh | en |
| dc.contributor.committeemember | Coutier-Delgosha, Olivier | en |
| dc.contributor.department | Aerospace and Ocean Engineering | en |
| dc.date.accessioned | 2024-12-18T09:00:26Z | en |
| dc.date.available | 2024-12-18T09:00:26Z | en |
| dc.date.issued | 2024-12-17 | en |
| dc.description.abstract | The filtered Rayleigh scattering (FRS) optical diagnostic has become an attractive technique for advanced aerodynamic measurements. The appeal of FRS is that it can simultaneously quantify density, temperature, and vector velocity. Additionally, it is entirely non-intrusive to the flow since the technique leverages how laser light scatters off of molecules naturally present in the gas. Acquired FRS data considered herein is in the form of a frequency spectrum. To process this data, a measurement model for the FRS spectrum is used, where inputs to this model are the flow field quantities of interest and the output is a representative FRS spectrum. An iterative procedure on these quantities is performed until the model spectrum matches the measured spectrum. However, as observed in certain applications of this technique, there is a range of measurement configurations where the standard methods to model this spectrum do not agree with measured spectra, even at known flow conditions. This disagreement causes large bias uncertainties in determined flow field quantities. This work leverages a data-driven approach to diagnose this disagreement by utilizing an extensive FRS database. Data analysis indicates that the widely used Tenti S6 model for the Rayleigh scattering lineshape is invalid in certain operating regions. A new Rayleigh lineshape modeling methodology, the Cabannes model, is introduced that vastly improves the agreement between measured and modeled FRS signals. Analysis of the Cabannes model indicates that one only needs to use this modeling methodology for FRS and not laser Rayleigh scattering (LRS). This improved measurement model can be used to mitigate bias uncertainties, and, in turn, improve the reliability of the FRS optical instrument. | en |
| dc.description.abstractgeneral | The filtered Rayleigh scattering (FRS) laser-based measurement technique has become an attractive tool for aerodynamic measurements. Leveraging the theory of Rayleigh scattering, measuring how laser light scatters off of air molecules can be used to determine the temperature, density, and velocity of the air. A specific combination of temperature, density, and velocity results in a unique, measured FRS signal. A computational model of this FRS signal is then used to go from FRS signal to those three quantities of interest. However, as observed by certain applications of this technique, there is a certain range of measurement cases where the standard methods to model this signal do not agree with measured signals at known values for temperature, density, and velocity of the air. This disagreement between modeled and measured signals causes large errors, and, therefore, decreases the reliability of this measurement for those cases. This work analyzes an extensive FRS database to determine the source of this disagreement. The conclusion from this data analysis is that the widely used computational model in the community is not correct for certain applications of this FRS measurement. A new method to model FRS signals is proposed in this work, which vastly improves the agreement between measured and modeled signals. This improved computational model can be used to remove the large errors seen in this FRS measurement system that were previously caused by modeling errors. This, in turn, will improve the reliability of this technique across the whole application space of applied aerodynamic measurements. | en |
| dc.description.degree | Doctor of Philosophy | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:42348 | en |
| dc.identifier.uri | https://hdl.handle.net/10919/123831 | en |
| dc.language.iso | en | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | Optical Diagnostics | en |
| dc.subject | Laser Rayleigh Scattering | en |
| dc.subject | Filtered Rayleigh Scattering | en |
| dc.subject | Measurement Modeling | en |
| dc.subject | Spectroscopy | en |
| dc.title | Unbiased Filtered Rayleigh Scattering Measurement Model for Aerodynamic Flows | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Aerospace Engineering | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |