Femtosecond laser tagging is demonstrated for the first time in R134a (1,1,1,2-tetrafluoroethane) gas and in mixtures of R134a with small quantities of air. A systematic study of this tagging method is explored through the adjustment of gas pressure, mixture ratio, and laser properties. It is found that the signal strength and lifetime are greatest at low pressures for excitation at both the 400 and 800 nm laser wavelengths. The relative intensities of two spectral peaks in the near-UV emission change as a function of gas pressure and can potentially be used for local pressure measurements. Single-shot precision in pure R134a is demonstrated in quiescent gas. One standard deviation (68%) of the uncertainty lies within of the mean velocity in a 0.1 atm pressure quiescent flow using a delay time of and within using a delay of . The variable parameter space is chosen to mimic conditions used in NASA Langley Research Center’s Transonic Dynamics Tunnel. Good signal-to-noise ratio is achieved for low-pressure conditions, especially in a pure freon environment. The precision and signal lifetime demonstrate the feasibility of using this technique for measuring representative Transonic Dynamics Tunnel flowfields in a bench-top laboratory setting.
Femtosecond Laser Tagging in R134a with Small Quantities of Air
AIAA Journal ; 57 , 5 ; 1793-1800
2019-05-01
Article (Journal)
Electronic Resource
English
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