Flow Measurements of Translational-Rotational Nonequilibrium Using Laser-Induced

Abstract. A shock wave impingement flow was studied under low temperature, low density conditions in a hypersonic free-jet wind tunnel [1]. A sharp-edged flat plate was placed at zero incidence in the hypersonic core of a free-jet of nitrogen gas at Mach 12; a right circular cylinder mounted in the middle of the plate projected out normal to the plate surface. The oblique shock produced at the plate leading edge impinged on the detached bow shock wave produced by the cylinder. The symmetry plane in the flow was studied using a laser sheet-beam probe from a narrow-bandwidth laser source, which induced fluorescence in iodine molecules seeded in the gas. Fluorescence patterns produced by the sheet-beam were recorded by a charge-coupled device camera as the laser frequency was tuned in increments over a range spanning two distinct absorption lines in the iodine spectrum. The fluorescence intensity-versus-laser excitation frequency data recorded at each pixel was least-squares fitted to a nonequilibrium model of the iodine spectrum to estimate local translational and rotational temperature, velocity, and density. Contour plots of these results are presented at a resolution equal to roughly one mean-free-path of the oncoming flow at the plate leading edge. Profile plots of translational and rotational temperature on the plate are presented