Browsing by Author "McDougall, Connor Charles"
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Item Open Access Aerothermodynamic Measurements in Hypersonic Non-Equilibrium Flows(2022-11-10) McDougall, Connor Charles; Johansen, Craig; Murari, Kartikeya; Morton, Christopher; Ghaemi, Sina; Davidsen, Joern; Bauwens, LucHigh enthalpy arc-jets are unique facilities particularly suited for producing complex flows in the aerospace field, such as the aerothermodynamics of a re-entry vehicle. Arc-jets are often used to evaluate important design factors that include heat shield materials and vehicle design. Characterization of these facilities is important, as studies often aim to match specific in-flight environments during experiments. Due to the complex environment produced by an arc-jet, with effects such as thermodynamic and chemical non-equilibrium occurring in the flow, characterization experiments are significantly more difficult than in conventional blow-down wind tunnels. The current work aims to characterize an arc-jet facility through spatially-resolved measurements of flow unsteadiness, temperature, and velocity. To achieve this goal, a non-intrusive imaging technique called “planar laser-induced fluorescence” was performed in the NASA Langley Hypersonic Materials Environmental Test System arc-jet facility. The experimental data was analysed to produce the quantitative measurements in multiple regions of the flow around a blunt body specimen. A three-temperature low fidelity numerical solver was created to simulate the flow in order to investigate thermal non-equilibrium effects occurring outside the imaging region in the arc-jet nozzle. Unsteadiness in the test section of the arc-jet was minimized by analyzing a subset of data assessing the gas injection configuration. Radial velocity, rotational temperature and translational temperature measurements are provided that can be used to validate future computational studies. The temperature measurements revealed rotational non-equilibrium occurring behind the bow-shock near the specimen surface. Computational results show the facility is capable of producing thermal non-equilibrium flow in the arc-jet nozzle. This work provides the first experimental and computational evidence of thermal trans-rotational non-equilibrium occurring in multiple regions of this arc-jet facility. Significant improvements to the methodology are also identified as recommendations for future arc-jet characterization studies.Item Open Access Quantitative Hypersonic Flow Measurements using Planar Laser-Induced Fluorescence(2018-09-10) McDougall, Connor Charles; Johansen, Craig T.; Kim, Seonghwan; Murari, Kartikeya; Wood, David H.The present work focuses on the development, testing, and assessment of several new quantitative analysis methods for nitric oxide planar laser-induced fluorescence experiments. The methods are based on performing a spectral scan with a pulsed laser, exciting multiple nitric oxide transitions,and analyzing the resulting spectra. The nitric oxide fluorescence spectra is processed using the developed quantitative analysis methods to produce temperature, mole fraction and heat flux. The temperature measurement is based on fitting a fluorescence model to the spectra from multiple transitions. The mole fraction measurement uses the fluorescence signal combined with the principle of conservation of mass. The heat flux measurement uses the principle of conservation of energy combined with temperature and velocimetry measurements. To assess these methods, experiments were performed at NASA Langley’s 31-in. Mach 10 wind tunnel, in Hampton Virginia, USA.A nitric oxide planar laser-induced fluorescence experiment investigating a hypersonic boundary layer was performed. The boundary layer was seeded with nitric oxide through a slot located nearthe leading edge. A pulsed laser was directed into the boundary layer from above, exciting the nitric oxide, and spectrally scanning across six fluorescence transitions. The data received from this experiment were processed using the quantitative analysis methods developed, to produce temperature, mole fraction and heat flux measurements. To assess the accuracy of the present methods,each quantitative measurement was compared to computational fluid dynamics (CFD) simulation results. Temperature measurements agreed with CFD predictions within 3-7% in most regions of the boundary layer. Mole fraction measurements agreed with CFD predictions within 6-10%and the heat flux measurement was approximately 26% lower than CFD results. Finally, important experimental design considerations are discussed to enhance these analysis methods in future applications. Overall, nitric oxide planar laser-induced fluorescence measurement methods are demonstrated and applied to a hypersonic boundary layer in a Mach 10 flow, with good agreement when compared to CFD results.