PLANAR VELOCITY-MEASUREMENT IN SYMMETRICAL FLOW-FIELDS WITH LASER-INDUCED IODINE FLUORESCENCE

A laser-induced fluorescence technique for time-averaged planar veloci ty measurements in nonreacting compressible flow is reported. The tech nique is based on the detection of fluorescence from a Doppler-shifted absorption line of iodine molecules seeded into the flow field. We ex ploit the symmetry of the investigated flow field to eliminate the col lisional impact shift from the measured total frequency shift of the i odine absorption spectrum. This reduces the amount of spectral data re quired for measuring two velocity components by a factor of 2 yet reta ins the accuracy of a counterpropagating laser sheets approach. The de monstration of this technique in a highly three-dimensional supersonic flow field represents what is to our knowledge the first planar veloc ity measurement with laser-induced fluorescence in which the contribut ion of the collisional shift is eliminated.