Date of Award
Master of Science in Optical Science and Engineering
Department of Engineering Physics
Kevin C. Gross, PhD.
Within the domain of chemical propulsion, the fields of combustion diagnostics and computational fluid dynamics each have a long history, and both have led to a better understanding of complex phenomena yielding practical improvements in propulsion systems. As more exotic forms of propulsion are developed, the importance of -- and often the challenges with -- both diagnostic and simulation capabilities also increase. In the case of scramjet combustion, these challenges primarily arise from the highly turbulent environment in the combustion cavity, and the high-speed, compressible nature of the flowfield. Efforts are underway to develop computer models of scramjet combustion environments to better understand the evolution of the flow field and heat transfer to the walls during combustion. This thesis effort experimentally supports these goals. Specifically, hyperspectral imaging measurements of an optically accessible scramjet were collected for different fueling rates. The primary focus was characterization the magnitude and dynamics of the outer window temperature in its response to combustion of different fueling rate. The outer window temperature was estimated via the radiometric brightness temperature -- a quantitative measure of infrared radiant emissions -- between 2000 cm-1 < ~v < 2250 cm-1 where the emissivity of the infrared-grade fused silica window is near unity and atmospheric absorption effects are minimal. Examining the radiant window emissions over a range of frequencies between 2500 cm-1 < ~v <4000 cm1, the spectral region in which the window transitions from opaque to transparent, reveals information related to the temperature gradient normal to the line-of-sight. A simple one-dimensional, numerical heat transfer model is used along with a spectral model for the window to interpret the temporal dynamics of brightness temperature in different spectral bands. Inferring the actual temperature profile would require temperature-dependent optical properties of fused silica over a broad, high-temperature regime, and at present these are unavailable. This work indicates there would be value in obtaining this optical data so that hyperspectral measurements of the scramjet could be used to quantify heat transfer to the side window. The window represents an important and dynamic boundary condition, and these hyperspectral measurements could be used to validate numerical simulations. Other work in this thesis effort explores qualitative differences in flowfield turbulence under different fueling conditions, and in principle this turbulence characterization could also be used to for comparisons with numerical simulations.
DTIC Accession Number
Kerst, Amy M., "Investigation of Scramjet Flowfield Temperatures at the Boundary Layer with Hyperspectral Imaging" (2018). Theses and Dissertations. 1758.