Thermal Nonequilibrium in Hypersonic Separated Flow

Abstract

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