Characterizing the accuracy of FLEET velocimetry using comparison with hot wire anemometry
2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Femtosecond Laser Electronic Excitation Tagging (FLEET) is used for velocimetry in a turbulent subsonic flow and the resulting measurements are compared with those captured using constant temperature hot wire anemometry. This study investigates the effects of optical properties (wavelength, pulse energy, beam focusing), imaging properties (camera delay, exposure time, averaging, magnification) and flow medium (air, pure nitrogen) on small-scale velocity measurements with FLEET. Parameters that contribute to higher emission intensity, such as pulse energy and focusing, tend to decrease velocity error but result in an asymmetric correlation function, suggesting perturbations from the laser-deposited energy. Tagging medium (air, nitrogen) primarily affects emission line thickness and signal- to-noise: lower velocity errors are found with pure nitrogen tagging. At the signal levels produced in this study, higher magnification tends to improve measurements overall, but increased magnification can feasibly introduce bias into measurements conducted at inferior SNRs.