Planar velocity measurement in symmetric flow fields with laser-induced iodine fluorescence

Abstract

A laser-induced fluorescence technique for time-averaged planar velocity measurements in nonreacting compressible flow is reported. The technique is based on the detection of fluorescence from a Doppler-shifted absorption line of iodine molecules seeded into the flow field. We exploit the symmetry of the investigated flow field to eliminate the collisional impact shift from the measured total frequency shift of the iodine absorption spectrum. This reduces the amount of spectral data required for measuring two velocity components by a factor of 2 yet retains the accuracy of a counterpropagating laser sheets approach. The demonstration of this technique in a highly three-dimensional supersonic flow field represents what is to our knowledge the first planar velocity measurement with laser-induced fluorescence in which the contribution of the collisional shift is eliminated.