Visualization of Two-dimensional Temperature Field in the Rarefied Gas Flow using I₂-PLIF

Abstract

A method for measurement of temperature in the rarefied gas flow has been developed. The flow field is visualized by planar laser-induced fluorescence (PLIF) of I ₂ seeded in carrier gas. Iodine molecules have many absorption lines in visible region and radiate intense fluorescence. The fluorescence intensity is proportional to the number density in the ground energy level excited by laser beam. This number is temperature dependent, so the local temperature can be decided from the ratio of the fluorescence intensities of two images obtained by laser beams with different wave length. This method allows to image the two-dimensional temperature distribution of the flow field by a laser sheet and a high sensitive CCD camera. In this paper, the optimum selection of two absorption lines in the transition of B³ Π₀⁺_u(ν'=43)←X ¹Σ+g(ν"=0) is provided theoretically and verified for the temperature measurement of the flow field of a supersonic free jet in which temperature varies drastically.