The RELIEF flow tagging technique and its application in engine testing facilities and for helium-air mixing studies
Additional Document Info
Raman excitation plus laser-induced electronic fluorescence (RELIEF) images the motion of oxygen molecules in air and other gas mixtures. This is accomplished by tagging oxygen molecules through vibrational excitation and imaging them after a short period of time by laser-induced electronic fluorescence. The vibrational lifetime of oxygen is sufficiently long and the signal sufficiently strong to allow this technique to be used over a wide range of flow conditions, from low subsonic to hypersonic, and in a variety of gas mixtures including high humidity environments. The utilization of a molecular tagging technique such as this is critical for environments in which seeding is impossible or unreliable and for measurements in which a wide range of scales needs to be observed simultaneously. Two experiments which have been conducted at national laboratories in medium- to large-scale facilities are reported. At the Arnold Engineering Development Center, RELIEF was used to examine velocity in a 1 m diameter tunnel for applications in the area of engine testing. At the NASA Langley Research Center, RELIEF is being used to examine supersonic mixing of helium in air in a coaxial jet in association with studies of fuel-air mixing in hypersonic engines. These applications are two examples of the wide range of practical uses for this new technology.
author list (cited authors)
Miles, R. B., Grinstead, J., Kohl, R. H., & Diskin, G.