Application of Molecular Tagging Velocimetry to Study Laminar-to-Turbulent Transition in Hypersonic Boundary Layers

This dissertation provides a comprehensive summary of quantitative streamwise velocity measurements in hypersonic boundary layers in a large-scale hypersonic test facility. These measurements are used to study the behavior of streamwise velocity in laminar hypersonic boundary layers and hypersonic boundary layers undergoing transition-to-turbulence. These measurements are made with and without the presence of an isolated cylindrical roughness element on a 20° wedge model. This dissertation provides a review of the theory of boundary layer transition-to-turbulence and of laser-induced fluorescence, which is the mechanism used to measure streamwise velocity non-intrusively. In addition to the streamwise velocity data, a comprehensive image processing method and uncertainty analysis method are presented.

The studies in this dissertation also detail the development of two fluorescence-based forms of the Molecular Tagging Velocimetry (MTV) technique for use at NASA Langley Research Center. The first is a single-laser excitation technique using fluorescence of nitric oxide (NO). The second is a three-laser technique where nitrogen dioxide (NO2) is dissociated with a high-intensity laser into NO and oxygen (O), with subsequent probing of NO fluorescence. The measurements presented in this dissertation are the first quantitative non-intrusive flowfield velocimetry measurements obtained in NASA Langley Research Center’s 31-Inch Mach 10 Air Tunnel.