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Calibration and Certification of Molecular Tracking for the Measurement of Near Wall Stresses in High Speed Unseeded Air and Nitrogen


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The Femtosecond Laser Electronic Excitation Tagging (FLEET) method is used for unseeded velocimetry in air and in other nitrogen-containing flows. FLEET enables tracking of the flow by writing and following line patterns as the move. Velocity measurements of a turbulent boundary layer were obtained for the calculation of skin friction. Comparisons between FLEET and hot wire anemometry, and analyses of turbulence statistics obtained with FLEET were performed in order to quantify perturbative effects of the tagging on small-scale turbulence. On the computational side, models were developed to follow the kinetics and to simulate the emission as a heated filament to better understand the effects of energy deposition and laser heating on the measurements. Efforts to enhance the FLEET tagging signal in different gas mixtures resulted in the discovery of argon as a promoter of higher signal intensities as well as new insight on the molecular processes. Zero-dimensional kinetics models were developed to determine the governing processes in the FLEET emission in different gas flows. Spin-off efforts at the Arnold Engineering Development Complex Tunnel 9 and NASA Langley have successfully demonstrated premiere boundary measurements in hypervelocity flows, and reflect FLEET's growing popularity as a diagnostic tool in the aerospace community.



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