Leading-Edge Separation in Thermal Nonequilibrium Hypersonic Flow

This project investigates the application of two diagnostic methods for the investigation of hypersonic separated flow in thermalnonequilibrium. This is part of a larger, international collaborative program to compare state-of-the art measurements of thethermal state of the flowfield with the best available computational predictions of the flowfield. This report discusses resonantlyenhanced shearing interferometry visualizations, using alkali metals as the resonant seed species. This visualization techniqueis tested for a low-density hypersonic separated flow around a ‘tick’-shaped leading-edge separated flow. Results for flowvisualizations are obtained using lithium metal and a broadband laser, lithium chloride salt with the same laser, and rubidiumchloride salt with a single-mode laser source. The differences in repeatability and image contrast for these three resonantlyenhanced techniques are discussed, and the establishment of the flow at a high-enthalpy condition produced in a shock tunnel isinvestigated using tunable diode laser absorption spectroscopy. The visualization comparison indicates that for the purposes ofvisualization, a broadband laser source using lithium metal provides the best sensitivity to density variations and the bestcompromise between resonant enhancement of refractivity and absorption of the laser light. The effects of included angle andleading edge radius are compared using the resonantly enhanced shearing interferometry, and compared to direct simulationMonte Carlo calculations. The diode laser measurements provided important information on flow duration and steadiness