Application of femtosecond-laser tagging for unseeded velocimetry in a large-scale transonic cryogenic wind tunnel

• Published in: Experiments in fluids 2021-05, Vol.62 (5), Article 99
• Main Authors: Reese, Daniel T., Thompson, Ryan J., Burns, Ross A., Danehy, Paul M.
• Format: Article
• Language: English
• Subjects: Cryogenic wind tunnels; Downstream effects; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Fluid- and Aerodynamics; Heat and Mass Transfer; Lasers; Marking; Model testing; Research Article; Signal to noise ratio; Two dimensional models; Velocimetry; Velocity; Velocity distribution
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-021-03191-x

Femtosecond laser electronic excitation tagging (FLEET) velocimetry was applied in the National Transonic Facility and assessed for its use in providing quantitative velocity measurements in a large-scale cryogenic wind tunnel. Comparisons of freestream results with theory and existing tunnel measurements indicate that FLEET velocity measurements agree within 1% of the tunnel reference, while the largest error among all conditions remained within 2.5%. For single-shot velocity measurements, binning of the FLEET intensity data improved the signal-to-noise ratio sufficiently to provide measurement precisions on the order of 1% of the freestream velocity. After confirmation of system performance, spatially resolved velocity profile measurements were obtained in the wake downstream of the Common Research Model wing. Effects of the model angle-of-attack on velocity deficit profiles were explored, and a two-dimensional, one-component velocity map resolving the wake region was constructed by scanning the laser’s position within the test section. The experimental campaign described herein represents the first non-intrusive, quantitative measurements of velocity made in this facility since its inception in 1984. Graphic abstract